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PHYSIOLOGY 


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Zhc  HDcbical  Epitome  Scries. 
PHYSIO  LOCIY. 


A  MANUAL  FUR  STUDENTS  AND  PRACTITIONERS. 


THEODORE    C.  GUENTHEK,  M.D., 

Asuislanl  Phi/sician,  Norwcffinn  Hospital,  Brooklyn:  ChitJ' of  MedU'al  Clinic,  Sorwegian 
Hospital  Dispenmry :  Member  of  Kino's  County  Medical  Society. 


AUGUSTUS   E.  CtUENTHER,  B.S., 

Formerly  Assistant  in  Physiology  id  the  Meilirnl  PepartmenI,  University  of  Michigan. 

SERIES    EDITED  BY 
V.  C.  PEDERSEN,  A.  M..  31.  D., 

Clinical  .{ssistnnt  in  Surgery  at  the  Sew  York  Polyclinic  Medical  School  and  Hosjiilal ; 
Deputy  Gcnito-Uriunry  Surgcan  to  the  Out-Paticnt  Departmnti  of  the  Xcw  York  Hospi- 
tal; Physiciitn-in-Charge,  .s7.  Chrysostoin' s  Dispeimiry  ;  Recently  Assistant  Demou- 
ttrator  of  .1  natomy  at  the  College  of  Physicians  and  Surgeons,  Columbia   I'ni- 
versity  in  the  City  of  Sew  York:  Assi.itant  .'^urgcon  to  the  Out-Patiait  De- 
partmctU  of  the  Roosevelt  Hospital  and  to  the  Vanderbilt  Clinic,  etc. 

ILLUSTRATED  WITH   FIFTY-SEVEN   ENGRAVINGS. 


LEA    BRD'IHKIJS   ,^-    CO.. 
PHILADELl'lII  A     AND    X  K  W     YoIJK:, 


0^74-0 
&^3 


Entered  according  to  Act  of  Congress,  in  the  year  1903,  by 

LEA   BROTHERS   &   CO., 

In  the  Office  of  the  Librarian  of  Congress.    All  rights  reserved. 


ELECTROTYPED  BV  PRESS    OF 

VESTCOTT  &.  THOMSON,    PHILADA,  WM.   J.    DORNAN,    PHILADA. 


AUTHORS'  PREFACE. 


It  has  been  the  aim  of  the  authors  in  the  preparation  of 
the  present  volume  to  gather  together  those  facts  of  Physi- 
ology with  which  medical  students  and  practitioners  should 
be  fannliar.  It  is  not  the  intention  to  produce  a  work  which 
shall   take  the  place  of   more   elaborate    text-books,  but  to 

f^    supplement  them  by  covering  the  essential  features  of  the 

^       subject. 

Theodore  C.  Guenther,  M.  D. 
J  Augustus  E.  Guenther,  B.  S. 

o  New  Yokk,  1903. 

J^  3 


EDITOR'S  rilEFACE. 


In  arrnngiiii!;  for  the  cditorsliij)  of  The  Medical  Epitome 
Series  the  publishers  (■st:il)li>lH'(l  a  few  simple  conditions, 
namely,  that  the  Series  as  a  whole  shoiihl  emhraee  the 
entire  realm  of  medicine;  that  the  individnal  volnnics 
shonld  authoritatively  cover  their  respective  subjects  in  all 
essentials;  and  that  the  maximum  amount  of  information, 
in  letter-press  and  engravings,  should  be  given  for  a  mini- 
mum price.  It  was  the  belief  of  publishers  and  editor 
alike  that  brief  works  of  high  character  would  render 
valuable  service  not  only  to  students,  but  also  to  practi- 
tioners who  might  wish  to  refresh  or  supplement  their 
knowledge  to  date. 

To  the  authors  the  editor  extends  his  heartiest  thanks  for 
their  excellent  work.  They  have  fully  justified  his  choice 
in  inviting  them  to  undertake  a  kind  of  literary  task  which 
is  always  ditHcidt — namely,  the  combination  of  brevity,  clear- 
ness, and  eom})rehensiveness.  They  have  equalled  the  con- 
scientious efforts  with  which  the  editor  has  performed  his 
duties  from  first  to  last.  Co-operation  of  this  kind  ought 
to  result  in  useful  books,  in  brief  manuals  as  contradistin- 
guished from   mere  eompends. 

In  order  to  render  the  volumes  suitable  for  quizzing,  and 
yet  ])r('serve  the  ('(mtinuitv  of  the  text  unbroken,  the  ques- 
tions have  been  gatluTcd  at  the  end  of  eacli  chapter.  This 
new  arrangement,  it  is  hoped,  will  be  convenient  alike  to 
students  and   j)ractitioners. 

Yktor  C.  Pedersen. 

New  York,  1903. 

5 


CONTENTS. 


CFI AFTER   I. 

PAGES 

General  Introduction 17-34 

I*hysiolih;y  and  IIiman  Physiology:  Fundamental  Proper- 
tie*  of  Living  Tliing8 17-19 

Celi^:  Their  Histological  Differentiation  and  Structure ;  Tlieir 
Essential  Part.s;  Tiioir  Reproduction  ;  Their  Origin  ;  Their 

Properties;  Their  Death 19-33 

The  Okujix  ok  Lifk 33 

Somatic  Death 33-34 


CHAFfER  II. 

Secretion 35-56 

Salivary  Glands 35-38 

Stomach 38-39 

Pancreas 39-40 

LiVKR 40 

Intestinal  Olaxds 41 

Serous  Secretions 41 

Lachry'mal  Glands 41 

Kidney  and  Urine 41-47 

Skin 47-18 

Mammary  Glands 48-50 

Thyroid    .    .    .    / 50-51 

Pancreas 51-52 

Si  rKARKN.vL  Capsules  (Adrenal  Bodies) 52 

Pituitary  Body 52-53 

Testis  and  Ovary 53 

Thymus  (Jland  ani>  Spleen 53-5t; 


8  CONTENTS. 

CHAPTER  III.  PAGES 

Digestion 66-71 

The  Peoteids 56 

The  Albuminoids 57 

The  CARBOHYDRA.TES • 57-58 

Water  and  Salts 58 

Oxygen 58-59 

The  Salivary  Secretion 60 

The  Gastric  Juice 61-62 

The  Pancreatic  Juice 62-63 

The  Bile 63-64 

The  Intestinal  Secretion 64 

The  Secretion  of  the  Large  Intestine 64-65 

Summary  of   Digestion  :    Proteids ;   Albuminoids ;    Carbohy- 
drates ;  Fats 65-67 

The  Self-digestion  of  the  Stomach 67-71 


CHAPTER   IV. 

Muscular  Mechanisms 71-80 

Mastication 71 

Deglutition .  71-72 

The  Movements  of  the  Stomach  and  Vomiting 72-73 

The  Movements  of  the  Intestines 73-74 

Defecation 75 

Micturition 75-76 

Parturition 76-77 

The  Locomotor  Mechanisms 77-78 

The  Voice 78-80 


CHAPTER  V. 

Absorption ■ 80-83 

General  Principles 80-81 

Absorption  from  the  Stomach 81 

Absorption  from  the  Small  Intestine 81-82 

Absorption  from  the  Large  Intestine 82-83 


coxrhwrs.  9 

C'llAlTKR    VI.  PAGFs 

Metabolism K:i-!tl 

TuK  KNEKtiY  OF  Imiod:  I'rottids  ;  All)iiiiiin<)i(ls  ;  Carholiydnitcs; 

Fat.s;   Water;  Salts S4-X;t 

TiiK  1)i;ti;i!M1nati()N  of  Mftaiiomsm .S<.)-'.)I 

cnAI'TKIl    Nil. 

The  Blood  and  Lymph 91-1U4 

TnK  Blooij  :  The  ('<)ri)ii.scle.s;  Ilieinoglobin ;  The  Pla.sma ; 
Combined  Proteids;  P^.\tr.ictives ;  Inorgjinic  Salts;  Coag- 
ulation or  Clotting 01-102 

The  Lymph 102-104 

CHAPTER  VIII. 

The  Circulation 104-13:^ 

TuK  llEAin-      104-121 

The  Arteriios,  Capill.\.rii->,  and  Veins 121-127 

The  PrLMoN.\.RV  CiRcrL.VTiox 127-130 

The  Circllation  of  Lymph 130-133 


CHAPTER   IX. 

Respiration 133-147 

The  Mechanical,  Physical,  Cikculatory,  and  Nervous 

Factors 133-14o 

Modified  Ri>piration:  Sighing;  Ilicenngh  ;  Cough  ;  Sneez- 
ing ;  Speaking  ;  Singing  ;  Sniffing  ;  Sobbing  ;  Laughing  ; 
Yawning ;  Sucking 145-147 

CHAPTER  X. 
Animal  Heat 148-152 

CHAPTER   XI. 

Nerve  and  Muscle 152-169 

Irritapility,  Conductivity,  and  Nutrition 152-153 

The  Independent  Contractility  of  Muscle 153-154 


10  CONTENTS. 

PAGES 

Irritatation  of  Nerve  and  Muscle  :  Mechanical ;  Ther- 
mal ;  Chemical ;  Physiological ;  Electrical 154-157 

Degeneration  of  Nerve  and  Muscle  :  Anodic  Closing 
Contraction ;  Cathodic  Closing  Contraction ;  Anodic  Open- 
ing Contraction  ;  Cathodic  Opening  Contraction     ....    157-158 

Muscle  Fatigue  and  Tetanus 159-164 

The  Energy  of  Muscle  Contraction 165 

The  Electrical  Currents  of  Muscle  and  Nerve  ;  Sec- 
ondary Tetanus 165-169 

CHAPTER   XII. 

The  Central  Nervous  System 169-205 

The  Structure  of  the  Nervous  System 169-173 

Reflex  Acts 173-178 

Voluntary  Acts 178-180 

Paralyses  and  Degenerations 180-181 

Areas  of  the  Cerebral  Cortex 181-184 

The  Function  of  Other  Parts  of  the  Encephalon  : 
Cerebellum ;  Thalamus  Opticus  ;  Corpora  Quadrigemina  ; 

Medulla 184-188 

The  Cranial  Nerves  :  Olfactory  ;  Optic  ;  Motor  Oculi ; 
Patheticus  ;  Trigeminus  ;  Abducens  ;  Facial ;  Cochlear  ; 
Glossopharyngeal ;  Vagus ;  Spinal  Accessory ;  Hypo- 
glossal     188-193 

The  Weight  and  Growth  of  the  Brain 193-196 

The  Fatigue  of  the  Brain 196-197 

The  Blood-supply  of  the  Brain 197 

Sleep 198 

Hibernation 199 

Hypnotism 199 

The  Knee-jerk 199-200 

The  Time  Involved  in  Nervous  Processes    ......   201-202 

The  Nerve-centres 202-205 

CHAPTER  Xin. 

The  Special  Senses 206-229 

Sight  :  Emmetropia  ;  Hypei-metropia ;  Myopia ;  Diplopia     .    206-219 


<.'n.\r/:.\Ts.  11 

PAOKH 

IlKARiNn 219-221 

TnK  Sknsk  of  K<jrii,iiiitirM 221-222 

Smki.i,  and  Tastk 222-224 

CiTANKors  Sknsation 224-22(> 

Common  Sknsation 220-229 


CIIAITEK    XIV. 
Reproduction 229-239 


APPENDIX. 


The  Chemical  Tests  of  Physiological  Analysis 241 

The  Metric  System  of  Units  and  their  Equivalents     .   .  242 

Comparative  Scales 243 


PHYSIOLOGY. 


CHAPTER   L 
GENERAL   INTRODUCTION. 

Physiology  is  the  science  that  treats  of  the  phenomeua  of  normal 
living  matter.  As  living  matter  may  be  either  of  animals  or  of 
plants,  so  there  is  a  separation  of  physiology  into  corresponding 
divisions — animal  and  vegetal)! e. 

Human  physiology  consists  of  those  facts  of  animal  physiology 
which  have  been  derived  from  experiments  upon  human  beings, 
together  with  much  that  has  been  ascertained  for  closely  allied 
animals  and  can  be  inferred  to  hold  true  for  man.  The  chemistry 
of  living  things  is  now  a  distinct  science, — physiolo<jl<-al  chemistnj, 
— although  it  was  not  so  formerly.  The  term  phiisiolog;/,  derived 
from  the  Greek  words  (J>'j^ci  and  ^ytyo^,  is  synonymous  etymologi- 
cally  in  its  broadest  application  and  acceptation  with  natural  phi- 
losophij,  and  the  earliest  physiological  conceptions  were  formed  in 
prehistoric  times,  inseparable  as  such  from  the  general  mass  of 
knowledge  which  during  the  course  of  later  centuries  grew  into 
theological,  scientific,  philosophical,  and  other  aggregations  of 
ideas. 

The  science  of  physiology  as  it  exists  to-day  has  been  gradually 
evolved  out  of  the  joint  labors  of  thousands  and  thousands  of 
workers.  Of  these,  there  are  some  that  stand  preeminent  and 
mark  in  a  way  the  principal  epochs  in  the  history  of  the  subject. 
In  the  earliest  times  among  the  philosophers  who  dealt  with  prob- 
lems that  are  now  physiological  may  be  mentioned  Empecheles, 
Hippocrates,  H'^racleitu.^  and  particularly  Arifitntle  (884-322  b.  c.\ 
Galpn  (131  to  about  200  a.  d.)  distinctly  recognized  the  nature 
and  importance  of  physiology.  His  system  of  medicine,  from 
which  the  physiology  of  the  time  is  inseparable,  held  an  almost 

2— Phvs.  17 


18  GENERAL  INTRODUCTION. 

indisputable  sway  for  nearly  thirteen  centuries.  Harvey  (1578- 
1657  A.  D.),  whose  name  stands  foremost  among  those  of  his  time, 
discovered  the  circulation  of  the  blood.  His  greatest  accomplish- 
ment was  the  establishment  of  the  experimental  method  in  physi- 
ology upon  a  firm  basis.  With  him  originated  the  conception 
"  omne  vivum  ex  ovo."  Haller  (1708-1777  A.  d.)  was  the  first  to 
recognize  the  necessity  of  bringing  together  the  mass  of  physiolog- 
ical facts  and  theories  that  had  arisen  during  the  sixteenth  and 
seventeenth  centuries  into  an  independent  science.  This  he  did  in 
his  Elementa  Physiologice  Corporis  Humani.  Johannes  Midler 
(1801-1858  A.  D.)  was  perhaps  the  greatest  physiologist  of  all 
times.  He  impressed  upon  his  science  the  general  form  or  aspect 
that  it  wears  to-day. 

The  aim  of  physiology  is  the  investigation  of  life.  The  term 
life  is,  however,  not  readily  definable.  In  general,  any  given 
piece  of  matter  is  said  to  be  alive  when  it  manifests  ihQ  fundor 
mental  properties  of  living  things.  These  properties  may  be  de- 
fined as  follows : 

1.  Irritability  is  that  property  of  protoplasm  which  enables  it 
to  undergo  characteristic  physical  and  chemical  changes  when 
acted  upon  by  certain  influences  called  stimuli.  Usually  there  is 
a  liberation  of  energy  in  the  response  out  of  all  proportion  to  the 
energy  applied  in  the  stimulus. 

2.  Conductivity  is  that  property  of  protoplasm  by  virtue  of 
which  a  condition  of  activity  aroused  in  one  portion  of  the  sub- 
stance may  be  transmitted  to  any  other  portion. 

3.  Contractility  is  that  property  of  protoplasm  which  enables  it 
to  change  its  form  when  irritated  by  stimuli. 

4.  Nutrition  is  that  property  of  protoplasm  which  enables  it  to 
convert  dead  food  material  into  its  own  living  substance. 

5.  Reproduction  is  that  property  of  protoplasm  which  enables 
it  to  separate  into  a  number  of  parts,  each  of  which  may  develop 
into  the  parent  form.  None  of  the  fundamental  properties  serve 
absolutely  to  distinguish  living  from  dead  matter,  since  all  are 
simulated  more  or  less  completely  by  phenomena  in  the  non-living 
world. 

Life  is  always  associated  with  a  peculiar  form  of  matter  called 
protoplasm,  and  is  never  found  elsewhere. 

Protoplasm  has  therefore  been  called  the  "physical  basis  of  life." 
It  may  be  defined  as  the  active  substance  of  which  living  things 


GESERAL   ISTRODUCTION.  19 

are  composed.  It  is  usimlly  colorless,  st'niiriuid  or  gelatinous  in 
coii.«ii:»teiu'y,  of  greater  retractive  |K)\ver  than  water,  and  granular 
in  apj)earance.  Consi:>ting  largely  of  water,  it  neverthele.-?!!  dot's 
nut  mix  with  water  a.<  long  as  it  i.s  living.  \\^  .specific  gravity  is 
greater  than  1  i  paraniM'ciurn,  1.2")),  hut  varies  in  many  organisms 
hv  the  formation  and  disapin^arance  of  vacuoles. 

The  jiuitl  initnrt'  of  protoplasm  is  shown — 

1.  By  the  streaming  phenomena  in  plant-colls  and  in  the  pseu- 
dojKnJia  of  rhizojxxls. 

'2.  By  its  formation  into  spherical  masses  whenever  it  is  freed 
from  its  cvU-walls. 

o.  By  the  assumption  of  a  spherical  form  hv  Huids  when 
iml)edded  in  a  mass  of  protoplasm.  Granules  and  all  for- 
eign suhstauces  lie  in  a  ijroiind  gub^tance,  which  at  times  is  per- 
fectly homogeneous,  but  usually  has  a  structure  resembling  a 
network. 

Of  the  many  attempts  to  explain  the  Ji if er  drncture  of  proto- 
plasm, that  of  Biitschli  is  the  most  successful.  According  to  this 
investigator,  protoplasm  is  an  emulsion,  the  vacuoles  or  globules 
of  which,  through  mutual  pressure,  according  to  well-known  math- 
ematii'al  principles,  give  rise  to  the  appearance  of  a  network. 
The  granules,  etc.,  never  lie  within  the  vacuoles,  but  always 
between  them.  Biitschli  has  imitated  in  every  detail  the  appear- 
ance of  protoplasm  by  artificial  emulsions.  These  were  prepared 
bv  mixing  intimatelv  cane-sugar  or  jxjtassium  carbonate  with  old 
oiive  oil.  A  minute  quantity  of  the  mixture,  placed  in  a  drop  of 
water  under  the  microsco|>e.  showed  not  only  all  the  peculiarities 
of  the  pr<itoplasmic  structure,  but  also  spontaneously  took  on 
ama^lvnd  movements. 

Protoplasm  is  not  a  chnnicnl  but  a  morphological  term — i.  > .,  it 
does  not  consist  of  a  definite  chemical  comjxnind,  but  of  the  <rreat- 
est  variety  of  substances,  some  of  which  are  the  most  complicate<l 
with  which  chemists  have  to  deal.  It  contains  cnrbohi/flrate.^  faf--*, 
uater,  mlh,  and  alwavs  proteid^  The  elements  which  are  present, 
— C,  N,  H,  O,  a  P,  01,  K.  Na,  >Ig,  Ca,  and  Fe— are  all  of  low 
atomic  weight.  Protoplasm  with  very  few  exceptions  is  divided 
into  microscopical  massi»s,  each  of  which  jx^si^esses  one  or  more 
ditTerentitited  portions  culled  a  ?*</rA  ;/>•. 

Such  a  mass  with  its  nucleus  is  a  cell.  .\  cell  may  be  defined 
as  the  elementary  unit  of  all  organisms,  no  matter  how  simple  or 


20  GENERAL  INTRODUCTION. 

how  complicated  they  may  be.  Every  organism  begins  its  indi- 
vidual history  as  a  cell  separated  from  a  preexisting  organism. 
From  time  to  time  this  cell  (ovum,  spore,  etc.)  divides  itself  into 
two  or  more  parts,  each  of  which  in  due  time  divides  again,  the 
resulting  divisions  in  every  case  forming  complete  cells.  In  the 
protozoa  the  daughter-cells  separate,  and  each  leads  an  independent 
existence,  but  in  many-celled  animals  they  remain  connected  and 
become  dependent  upon  one  another. 

A  histological  differentiation  takes  place  as  the  animal  develops, 
so  that  they  form  groups  of  cells  which  are  totally  different  in 
appearance,  and  results  in  tissue-  and  organ-formation.  They  take 
on  different  functions,  p)(^^^  i^assw,  and  one  group  of  cells  will 
perform  a  certain  work  for  the  good  of  the  entire  economy. 
They  thus  lose  their  individuality  and  become  dependent  upon 
one  another.  This  is  known  as  the  j^hysiological  division  of 
labor. 

The  exact  molecular  structure  of  living  matter  is  unknown, 
but  there  is  no  doubt  that  it  is  of  very  great  complexity.  It  dif- 
fers from  dead  protoplasm  in  its  unstable,  labile  nature,  reacting 
to  an  enormous  number  of  substances  which  are  indifferent  to 
dead  protoplasm.  It  manifests  a  continual  tendency  to  undergo 
changes,  while  dead  protoplasm,  if  protected  from  external  agen- 
cies, can  be  kept  indefinitely.  The  nitrogen-containing  oxidation 
products  derived  from  the  two  are  radically  different.  Those  from 
living  matter — uric  acid,  creatin,  adenin,  xanthin,  guanin,  etc. — 
are  all  characterized  by  the  possession  of  the  cyanogen  group,  CN. 
This  group  is  one  of  great  internal  energy,  so  that  compounds 
containing  it  have  a  marked  tendency  to  undergo  dissociation. 
This  is  especially  the  case  in  the  presence  of  oxygen.  It  is  a  well- 
known  fact  that  cyanogen  compounds  also  have  the  jjroperty  of 
polijmerization — that  is,  of  combining  with  compounds  having  a 
structure  like  their  own,  so  as  to  form  more  complex  combinations. 
By  this  process  they  become  less  and  less  stable,  until  the  insta- 
bility reaches  its  acme  by  the  introduction  of  oxygen,  when  the 
compound  undergoes  a  breaking-down  process  resulting  in  the 
formation  of  simpler,  more  stable,  bodies.  The  act  of  dissociation 
liberates  energy,  which  appears  in  the  manifestations  of  life. 
Pfliiger  has  suggested  that  in  the  change  from  living  to  dead  pro- 
toplasm the  cyanogen  grouping  is  converted  to  the  inert  ammonia 
grouping  by  the  absorption  of  water.     It  is  convenient  to  designate. 


GENERAL  INTRODUCTION.  21 

the  exju-ef^siou,  mass  of  liviiij;  matter,  hy  the  shorter  terms  hliii/t'ii 
or  hiujjluiiin.  Bij  biixjcn  m  itndrrdood  the  umallcd  qiiunt'dy  oj  /ivlmj 
matter  that  can  manifest  the  property  of  nutrition. 

That  part  of  nutrition  desi}^Miated  as  metabolism  is  the  most 
charaeteristic  of  all  the  properties  of  living  matter.  By  it  is 
meant  the  total  series  of  changes  hy  which  siihstanees  are  huilt  uj) 
into  living  matter  {(iiKiho/i^'^in  )  and  again  broken  down  (  kutdbolixiii ). 
Anaholism  and  kataholism  have  op[)osite  elfects  on  living  matter, 
hut  they,  nevertheless,  go  on  simultaneously  in  the  same  cell,  and 
under  normal  conditions  are  always  active.  When  they  e<jual  one 
another  the  cell  is  at  rest — a  conclition  that  has  been  called  (ntltm- 
omous  eqnilibrium.  If  auabolLsm  is  in  excess  of  kataholism,  the 
cell  increases  in  bulk  or  grows,  while  an  excess  of  kataholism  over 
anal)olism  will  result  in  atroph.v.     The  relations  of  anaholism  to 

A 

katai)()lism  may  be  expressed  by  the  symbol  "    .     There  is  no  rea.son 

to  suppose  that  biogens  are  all  of  the  same  structure  ;  on  the  con- 
trary, they  are  probably   as  numerous  as  the  cells  have  different 

A 

functions.     Therefore  the  relation  —  is  more  correctly  expressed  as 

'  '     '       j*       *  '  '  '-,   where  each   of  the   foctors  a,,   a.„  a....  and 
d,-\-d,-^d,+d,...'  .     . 

rf,,  r/.„  f/^,  .  .  .  may  vary  independently  of  the  others  and  within 
very  wide  limits  as  the  case  may  be. 

In  anv  given  cell  where  processes  of  one  kind  are  in  exce.«s 
over  the  other,  a  reaction  arises  which  rendere  the  biogen  more 
resistant  to  further  change  of  the  same  character,  and  favors  a 
tendency  in  the  other  direction.  If,  for  instance,  anabolic  changes 
have  been  called  out  in  a  cell  by  a  stimulus,  they  generate  in  time 
an  acceleration  of  kataholic  proces.ses  until  the  two  are  in  equi- 
librium. The  general  condition  of  the  cell,  however,  is  above  par, 
and  is  called  aJIonnmnii>i  eqnih'hrliim.  When  the  stimtilus  is  re- 
moved, anabolic  processes  are  lessened,  and  therefore  increa.*«ed 
kataholism  now  decreases  also  ;  but  kataholism,  although  decreas- 
ing, is  in  excess,  and  its  reaction  tends  to  increase  anabolic  proc- 
eisses  until  both  are  in  equilibrium.  There  is  thus  an  internal 
self-ad}}ist)nent  of  metabolism  in  living  matter.  It  must  be  borne 
in  mind  that  metabolism  is  probably  not  limited  to  the  building-up 
and  breakintr-down  of  the  bio<ren,  but  mav  be  brouirht  about  in 


22  GENERAL  INTRODUCTION. 

other  substances  uuder  the  influence  of  living  matter.  Such 
changes  are  designated  contact  changes. 

In  order  that  metabolism  may  continue  living  matter  must  have 
a  sufficient  supply  of  such  material  as  it  can  build  into  its  struc- 
ture. These  materials  are  called  foods,  and  may  be  defined  as 
substances  which,  taken  into  the  cell,  aid  in  the  repair  or  in  the 
formation  of  new  biogens,  adding  to  the  sum-total  of  energy 
which  the  cell  may  liberate,  and  are  finally  cast  oflT  by  the  cell  in 
altered  chemical  condition.  The  taking-in  of  food  by  an  organism 
is  termed  ingestion.  In  very  few  cases  is  the  ingestion  of  solid 
foods  possible,  so  that  in  order  that  they  may  be  made  use  of  they 
are  digested — i.  e.,  they  are  acted  upon  by  complex  nitrogenous 
bodies  known  as  ferments  or  enzymes,  which  convert  them  into 
soluble  forms.  Enzymes  are  the  products  of  animals  and  plants 
possessing  the  power  of  producing  chemical  changes  in  other 
bodies  without  apparently  undergoing  any  change  themselves.  As 
the  conversion  takes  place  within  or  without  the  protoplasm  it  is 
designated  as  intra-  or  extra-cellular  digestion. 

The  steps  through  which  dead  matter  passes  in  its  synthesis  to 
living  matter  are  very  incompletely  known.  In  green  plants 
which  thrive  on  the  inorganic  compounds,  carbon  dioxide,  water, 
and  simple  nitrogenous  salts,  the  first  step  is  observable  in  the 
cells  of  the  leaf,  where,  under  the  influence  of  chlorophyll  and 
the  energy  of  the  sun's  rays  (yellow  chiefly),  the  carbon  dioxide 
of  the  air  is  split  into  its  elements  and  the  carbon  is  united  with 
hydrogen  and  oxygen  in  the  proportions  of  water  to  form  starch 
(CgHjpOg),^.  The  latter  is  visible,  microscopically,  as  minute  gran- 
ules, and  its  formation  has  been  proved  to  go  hand-in-hand  with 
the  disappearance  of  carbon  dioxide.  This  forms  the  starting- 
point  for  the  formation  of  all  other  bodies  in  the  plant.  Recon- 
verted to  sugars  probably,  it  disappears  from  the  cells,  is  united 
with  nitrogen,  which  has  been  taken  into  the  plant  in  the  form  of 
nitrites  and  nitrates,  and  is  finally  built  into  the  structure  of  liv- 
ing matter.  The  successive  steps  are  not  known.  Animals  cannot 
live  on  inorganic  salts,  but  require  their  nitrogen  in  the  form  of 
proteids,  and  in  this  sense  are  dependent  upon  plants  for  continued 
existence. 

The  Nucleus. — In  all  cells  the  presence  of  a  nucleus  or  nuclear 
matter  is  indispensable  to  metabolism.  Nucleus  and  protoplasm 
separated  from  each  other  very  quickly  degenerate. 


(1 ES  EIL 1 L   1 S  TIWDU(  "I'l  O  S.  23 

Cell-growth. — Tlie  fonnttflim  of  new  bior/enx  or  growth  takes 
|)l;i(v  oiilv  wlioii  mu'lcar  iimtter  is  nornmlly  present,  and  eon- 
tiiiiie.s  until  the  cell  liaa  ri-aelietl  its  iiiaxiinuMi  si/c  At  tlii.s  stage 
the  extent  of  surfaee  of  the  cell  (ietcrniinin^'  tiie  ijuanlity  of  nutri- 
ment that  can  he  al)sorl)ed  is  insuliicieiit  to  supply  the  mass  of 
living  matter.  Such  a  point  is  always  reached,  sooner  or  later, 
hecause,  iis  the  cell  grows,  the  surfaee  increases  only  as  the  ntjnare 
while  the  volume  increases  as  the  cube  of  their  like  dimensions. 
Reproduction  now  takes  place,  which  has  ai)propriately  heen 
termed  '' dixroiitiniwus  growtlL'  It  is  always  essentially  a  sepji- 
ration  from  the  body  of  an  individual  of  a  portion  of  its  own 
material,  which  under  proper  conditions  grows  into  an  adult  organ- 
ism. In  man  growth  continufjs  from  the  segmentation  of  the 
ovum  to  about  the  age  of  twenty-five,  and  is  increased  by  system- 
atic exercise.  It  consists  not  oidy  of  an  enlargement  and  multi- 
plication of  cells,  but  of  a  deposition  also  of  intercellular  material. 
It  may  be  divided  into  an  embrijonie  period,  a  fcdal  period,  infancy, 
childhood,  youth,  maturity,  and  old  age.  As  growth  progresses, 
the  capacity  for  more  growth  lessens. 

Reproduction. — There  are  two  distinct  methods  of  reproduction, 
— the  asexual  and  the  sexual. 

Asexual  procreation,  or  agamogenesis,  is  the  chief  method  iu 
unicellular  organisms,  and  the  sole  method  iu  the  multiplication 
of  tissue-cells.  It  consists  of  the  formation  of  offspring  through 
the  activity  of  a  single  parent.  An  amoeba,  for  instance,  will  ex- 
hibit a  gradual  lengthening  of  the  nucleus,  followed  by  a  con- 
striction at  the  equator  of  the  long  axis,  so  that  it  assumes  the 
shape  of  a  dumb-l)ell.  and  by  a  progressive  deepening  of  the  con- 
striction is  finally  separated  into  two  portions.  The  protoplasm 
now  becomes  separated  into  two  parts  in  a  similar  manner  by  the 
formation  of  a  furrow  running  around  the  ama'ba,  and  falling 
into  the  same  plane  as  the  constriction  of  the  nucleus.  There 
arise,  in  this  manner,  two  nucleated  masses  of  protoplasm  which 
lead  an  independent  existence  and  in  turn  divide  again.  This  is 
known  as  simple,  direct,  or  amitotic  division. 

When  cells  divide,  there  are,  however,  generally  present  com- 
plicated changes  of  the  nucleus,  giving  rise  to  indirect,  mitotic,  or 
karyokiiietic  division.  The  ordinary  resting  nucleus  undergoes 
changes,  so  that  the  chromatic  substance  is  transformed  into 
threads  of  equal  length  loosely  coiled  together.     Simultaneously 


24 


GENERA  L  INTR  OD  UCTION. 


there  occur  a  disappearance  of  the  nucleoli  and  of  the  nuclear 
membrane,  while,  radiations  in  the  cytoplasm  of  the  cell  at  oppo- 
site sides  of  the  nucleus  mark  the  positions  of  the  centrosomes. 
This  stage  is  known  as  the  mother-skein.  Each  of  the  chromatic 
threads  now  divides  lengthwise,  so  as  to  appear  double.  They 
grow  shorter,  become  V-shaped,  and  arrange  themselves  about  the 
equator  of  a  spindle  which  has  been  formed  between  the  centro- 


FlG.  1. 


Amoeba  polypodia  in  six  successive  stages  cif  division  (after  F.  E.  Schultze,  from 

Verwornj. 

somes,  extending  from  one  to  the  other.  The  free  ends  of  the 
chromatic  filaments  point  outward,  so  that  they  have  the  appear- 
ance of  a  wreath  or  star  which  gives  to  this  the  name  of  the 
mofher-ivreath  or  aster  stage. 

The  third  stage  consists  in  the  migration  of  the  segments,  during 
which  the  apices  of  the  divided  chromatic  filaments  separate  from 
one  another  and  move  toward  their  respective  centrosomes,  around 


aESKi:. I  /.    IXTPiODl TTfON. 
a  li(i.  "J.  '' 


25 


Pchcmntii-  n-priMiiiaiion  of  mitotic  niioli'iir  divisidii  inliir  I'li-iniiiinp,  from  Ver- 
\V(irii>:  (I,  Miitlur-skiin  >taf;o :  '>.  aster  stage;  c  and  d,  mignuion  of  chromosomes  ; 
( ,  liiustrr  .stu;;f  ;  /,  (liiiij^'hlcr-i-olls. 


26  qenehal  introduction. 

which  they  group  themselves  to  form  the  daughter-wreaths  or  dias- 
ter  stage.  The  cytoplasm,  while  the  above  changes  are  taking 
place,  has  become  constricted  by  a  marked  furrow  running  about 
the  cell  in  a  plane  at  right  angles  to  the  long  axis  of  the  spindle. 
The  gradual  deepening  of  the  furrow  separates  the  cell  into  two 
parts.  During  this  time  each  of  the  daughter-wreaths  undergoes 
retrogressive  changes  leading  to  the  formation  of  ordinary  resting 
nuclei.  The  connecting  filaments  of  the  spindle  and  the  polar 
radiations  disappear.  The  chromatic  threads  lengthen  and  be- 
come loosely  coiled  together  ;  a  nuclear  membrane  is  reformed, 
and  nucleoli  make  their  appearance. 

Sexual  reproduction,  or  gamogenesis,  is  the  most  wide-spread 
form.  When  it  occurs  in  unicellular  organisms,  it  is  known  as 
conjugation.  Two  individuals,  paramoecia  for  example,  assume 
positions  parallel  to  each  other,  and  a  fusion  of  their  protoplasm 
takes  place  at  their  oral  openings.  Ciliates  have  two  kinds  of 
nuclei — a  macro-  and  a  micro-nucleus.  The  former  degenerates  in 
each  individual,  but  the  latter  divides  twice  in  succession.  Three 
of  the  resulting  daughter-nuclei  go  to. pieces,  but  the  fourth  divides 
once  more,  thus  forming  two  nuclei  for  each  cell.  Now,  one  of 
each  pair  of  the  nuclei  migrates  into  the  other  cell  through  the 
bridge  of  connecting  protoplasm,  and  fuses  with  the  nucleus  which 
has  remained  there.  The  combination-nucleus  now  divides  twice 
in  succession,  while  the  cells  separate  from  each  other  and  divide 
also.  Each  daughter-cell  has  two  nuclei  which  grow  into  the 
macro-  and  the  micro-nucleus. 

In  the  higher  animals  reproduction  is  more  specialized.  There 
exist  two  kinds  of  sexes,  male  and  female,  each  of  which  consists 
of  two  groups  of  cells — somatic  cells  and  germ  cells.  The  latter 
serve  for  reproduction,  while  the  former  serve  all  the  other  func- 
tions of  the  body.  The  male  and  female  germ-cells  differ,  the 
former  being  small  and  active,  while  the  latter  are  comparatively 
large  and  passive.  The  fusion  of  their  nuclei  is  the  essential  part 
of  reproduction  and  is  known  as  fertilization.  In  some  metazoa 
the  germ-cells  of  the  female  may  undergo  development  without 
fertilization,  which  is  known  as  parthenogenesis. 

The  significance  of  fertilization  has  been  much  discussed.  There 
are  several  views  : 

1.  That  it  rejuvenates  the  protoplasm,  renewing  its  power  to 
divide  asexual  ly. 


GKSKHAl.   ISTllohrcTlnS.  27 

2.  That  roprodiK'tioM  prcvciit.s  variation  ami  preserves  the  uiii- 
f'orinity  ot"  tlie  racv. 

.'{.   That  by  iVt'sh  coinbinatioii.s  it  Lfives  rise  to  variations. 

The  living  matter  of  the  fertilized  ovum  is  acted  upon  by  two 
forces — heredity,  wliich  preserves  its  characteristics,  and  athiptn- 
tioii,  which  changes  tliem.  Heredity  includes  the  transmission  of 
both  actual  and  jniteiiiial  characteristics  from  [nirents  to  oH'spring. 
The  resemblance  is  most  complete  between  child  and  parent,  and 
tiiminishes  directly  backward  along  the  ancestral  line.  The  re- 
send)lances  may  be  inKitmnica/,  j>lnj,siol()(/lca/,  or  jtxijelto/tjtjica/,  or 
all  three  variously  combined  and  related.  Characters  that  d(j 
not  appear  in  the  jjarent,  but  are  transmitted  from  grandparent 
to  child,  are  called  latent  and  give  rise  to  atavimn  or  neersioit. 
Tkia  occurs  mod  often  when  two  strains  are  crossed ;  thus  half-castes 
are  usually  more  degraded  than  either  their  civilized  or  savarje 
parent. 

The  inheritance  of  (ic^n/rer/  rharacter.'<  is  a  problem  that  has  not 
yet  been  solved.  It  cannot  be  denied  to  exist  in  unicellular 
oriranisms,  where  the  protoplasm  of  the  parent  becomes  directly 
that  of  the  offspring.  In  the  human  being,  cases  of  transmissal 
of  acquired  characters  can  be  explained  otherwise.  However, 
germinal  infections  of  syphilis  can  take  place  through  the  ovum 
or  spermatozoon.  Intra-uterine  infections  of  typhoid,  scarlatina, 
endocarditis,  small-pox,  measles,  croui)()Us  pneumonia,  and  anthrax 
have  been  okserved  to  take  place,  but  these  are  not  comparable 
to  a  modification  of  the  germ-plasm  through  heredity  in  the  ordi- 
nary sense. 

The  basis  of  heredity  lies  undoulitedly  in  the  substance  of  the 
germ-cells.  Home  biologiists  maintain  that  the  chromatic  is  the 
sole  germinal  substance.  Others  regard  both  protoplasm  and 
nuclear  matter  as  essential,  since  the  characteristics  of  every  cell 
depend  upon  its  metabolism,  and  this  in  turn  depends  upon  the 
integrity  of  protoplasm  and  nuclear  matter.  Whatever  the  basis 
is,  it  may  be  designated  as  rjmn-jidisni. 

The  origin  of  germ-plasm  is  ex])lained  by  two  views: 

1.  It  may  arise  from  small  particles,  r/cnuuuli's  (''  lift/r  (/rrm-':'' ), 
given  off  from  the  various  cells  of  the  body  ami  collected  into 
germ-cells. 

2.  It  may  not  be  formed  in  the  body,  but  bi-  siinplv  transmitted 
from  generation  to  generation,  an<l  be  directly  continuous  from  one 


28  GENERA  L  INTR OD  UCTION. 

individual  to  another.  In  this  case  parts  of  the  body  are  deriva- 
tives from  the  germ-plasm  and  cannot  return  to  their  primitive 
condition. 

There  are  also  two  views  as  to  the  structure  of  germ-plasm : 

1.  That  it  possesses  a  complicated  structure  and  contains  the 
rudiments  of  the  cells,  tissues,  and  organs  of  which  the  body  is 
composed.     This  may  be  called  the  theory  of  preformation. 

2.  That  germ-plasm  is  isotropous, — i.  e.,  one  part  is  essentially 
like  every  other  part, — and  that  histological  differentiation  is  the 
result  largely  of  external  influences.  This  is  called  the  theory 
of  epigenesis.  The  transmission  of  hereditary  characters  is  not  so 
complete  that  the  offspring  are  absolutely  like  their  parents. 
Every  individual  varies  a  little  from  every  other.  These  varia- 
tions are  either  acquired  subsequently  to  fertilization  or  are  inher- 
ent in  the  germ-plasm.  Those  of  the  germ-plasm  are  due  to 
nutrition  and  to  sexual  reproduction.  Having  granted  variations 
of  germ-plasm  which  produce  divergencies  in  the  adult  organism, 
Darwin  has  shown  that  in  the  struggle  for  existence  all  those  indi- 
viduals most  closely  adapted  to  their  environment  survive  in  the 
long  run  and  produce  most  offspring  which  in  turn  inherit  the 
same  favorable  characters.  Those  not  so  well  adapted  to  their 
environment  gradually  become  extinct.  There  arises  thus  a 
selection  of  those  most  fitted  to  live,  which  is  termed  natural  selec- 
tion. 

The  fertilized  germ-cell  undergoes  a  series  of  changes  by  which 
it  becomes  more  complicated,  and  w^hich  constitutes  its  life-history, 
or  ontogeny.  Through  heredity  those  of  one  organism  are 
closely  similar  to  those  of  another  of  the  same  species.  But  by 
adaptation  through  variations  and  through  natural  selection 
groups  of  organisms  begin  to  differ  in  their  ontogeny,  and  conse- 
quently in  their  adult  state,  so  that  they  in  time  form  distinct 
species.  This  has  taken  place  with  all  life  on  the  earth,  and  these 
changes  in  toto  constitute  phylogeny.  Phylogeny  is  the  result  of 
the  same  factors  as  ontogeny.  In  fact,  ontogeny  is  an  abbreviated 
history  of  phylogeny,  modified  to  some  extent  by  secondary  adap- 
tations. 

Cell  Stimulation. — Living  matter  is  responsive  to  various 
changes  in  its  environment  which  are  called  stimuli.  These  may 
be  grouped  into  mechanical,  thermal,  photic,  electrical,  and  chemical 
stimuli.     Each  may  produce  either  of  two  results.     If  the  normal 


ahWh'iLir  isrnoDrcTioy.  20 

phenomena  are  intensitied  or  incrcasi'd  (nianlitatively,  the  result 
is  called  an  crrUntioii.  It"  lliey  are  ilecreasi-d,  it  is  called  an  ;'/////- 
hiiiiiii.  It  is  possilile  that  the  nature  of"  the  phenomena  may 
change  in  eluiraeter,  giviui^  rise  to  tirrrohioiic jihiiiomcna,  such  as 
are  seen  iu  /V//<//  or  atui/foid  (!('(/> iicnition.  Kxamples  of" excitatiou 
by  various  stimuli  are  very  familiar. 

The  most  obvious  result  of  the  actidn  of  rhcmicuh  is  seen  in  the 
production  of  movements.  If,  for  instance,  there  are  addeil  to  a 
medium  containini^  amteine  a  tew  drops  of  a  weak  solution  of  an 
acid,  alkali,  or  salt,  the  activity  of  the  animals  is  at  first  increased, 
but  soon  their  psi'udo|)()ds  are  retracted  and  they  take  on  a  more 
or  less  spherical  shape.  The  same  effects  are  produced  in  other 
organisms  possessing  pseudopodia,  while  the  cilia  of  infusoria  have 
their  movements  enormously  increased.  Various  forms  of  muscle- 
fibres  (myoides,  smooth  and  striatetl  muscles)  contract  and  tend  to 
take  on  a  spherical  form.  Crystals  of  .<odium  chloride  applied  to 
the  motor  nerve  of  a  muscle  will  produce  an  irregular  series  of 
twitches.  In  this  connection  may  be  mentioned  a  curious  phenom- 
enon observed  by  Bieilermann.  If  the  sartorius  muscle  of  a  frog 
is  immersed  in  a  solution  of  5  grammes  of  sodium  chloride,  2 
grammes  of  sodium  phos()hate,  and  •]  gramme  of  sodium  carbonate 
iu  a  litre  of  water  at  a  temperature  of  from  3°  to  10°  C,  the 
muscle  will  fall  into  rhi/thmie  contractions,  which  are  never  to  be 
observed  in  the  muscle  under  normal  conditions. 

Chemical  stimnhdion  maij  cauM'  active  relaxation  a.t  well  as  co)i- 
tractioti.  Amadxe  and  myxomycetes.  when  deprived  of  oxvgen, 
gradually  cease  all  nKn'ement,  but  when  oxygen  is  again  provided, 
marked  activity  is  manifested  in  that  the  protoplasm  moves  toward 
the  source  of  oxygen  by  the  extension  of  its  pseudopodia.  Living 
matter  may  be  stimulated  by  chemicals  in  other  ways.  Many 
marine  organisms  like  the  flagellate  noctiluca  are  capable  of  pro- 
ducing light.  If  to  a  quantity  of  sea-water  containing  such  ani- 
mals a  drop  of  distilled  water,  concentrated  solutions  of  salt.s 
acids,  alkalis,  etc.,  are  gently  added,  they  will  occasion  the  pro- 
duction of  a  slowly  increasing  circle  of  light  as  the  diffusing  sub- 
stance gratlually  spreads  out. 

It  has  lieen  shown  by  Voit  that  an  adult  hard-working  man  re- 
quires about  lis  grammes  of  proteid  in  order  that  he  mav  not 
lose  weight.  This  amount  is  daily  broken  down  to  furnish  energv 
expended  in  his  work.      If  the  amount  of  proteid  is  now  increased. 


30  GENERAL  INTRODUCTION. 

the  excess  is  not  necessarily,  as  might  be  expected,  built  up  into 
the  structure  of  his  body,  but  is  metabolized  and  excreted  as 
urea,  etc.  It  is  assumed,  in  this  case,  that  the  excess  of  pro- 
teid  has  stimulated  both  auabolism  and  katabolism.  A  super- 
abundance of  carbon  dioxide  supplied  to  a  chlorophyll-containing 
plant  stimulates  metabolism  and  leads  to  an  increased  production 
of  starch.  In  many  cases  chemical  substances  stimulate  anabo- 
lism  more  than  katabolism.  This  is  particularly  true  during  the 
growing  years  of  a  child.  Pathology  offers  many  examples  of 
what  are,  very  probably,  instances  of  chemical  stimulation  where 
a  rapid  multiplication  of  cells — of  the  epidermis,  for  example — 
leads  to  the  formation  of  tumors. 

Meclianical  stimulation  includes  all  alterations  of  pressure,  no 
matter  how  produced,  to  which  living  matter  is  subjected.  The 
slightest  touch  applied  to  the  pseudopodia  of  a  rhizopod  will  cause 
their  retraction.  An  amojba  under  stronger  stimulation  becomes 
spherical.  In  many  cases,  as  in  actinospherium,  a  rapid  secretion 
of  a  sticky  material  takes  place,  which  serves  normally  to  hold 
small  infusoria  that  constitute  food  for  this  organism.  Stentor 
and  vorticella,  when  touched,  withdraw  from  the  source  of  irrita- 
tion with  lightning-like  rapidity.  Smooth  and  striated  muscle- 
fibres  contract  when  struck  by  a  sharp  blow.  Phosphorescent 
organisms  of  the  ocean  reveal  their  presence  whenever  the  water 
is  disturbed.  The  rhythmic  movements  of  the  cilia  of  ciliates 
are  accelerated  and  increased  in  amplitude  by  mechanical  stim- 
ulation. 

Any  sudden  marked  change,  whether  of  an  increase  or  decrease, 
in  the  temperature  of  the  medium  surrounding  an  organism  will 
act  as  a  stimulus.  Slow  changes  act  differently.  There  is  an 
average  temperature  to  which  any  given  organism  is  subjected. 
It  may  be  stated  as  a  general  rule  that  every  increase  above  the 
average  up  to  a  certain  maximum  temperature  will  cause  in- 
creased activity,  while  a  decrease  in  temperature  causes  an  oppo- 
site result.  A  good  example  is  to  be  found  in  the  formation  of 
alcohol  and  carbon  dioxide  from  grape-sugar  through  the  action 
of  yeast-cells.  Cold-blooded  animals,  frogs  and  salamanders,  be- 
come lively  during  warm  and  very  inactive  during  cold  weather, 
which  is  correlated  with  corresponding  metabolic  changes.  Warm- 
blooded animals,  however,  by  means  of  the  mechanisms  which 
regulate  and  maintain  a  high  internal  temperature,  show  an  in- 


GKSr.llAL    ISTllOl'rCTlOS.  31 

croiisod  inotnbolisiii  in  (-old  wcatlicr,  lliiis  pi-DviiiLf  an  cvccjitidii 
Id  the  IbiTiioiiiL''  nilc. 

(irowtli  of  varioiir^  oriraiiisiiis  is  <rreatly  iiilliiciiced  l»y  temper- 
ature. Seeds  l)e,ij:iii  to  germinate  only  when  tlie  warmth  has 
reaelied  a  certain  point:  tliis  for  Indian  corn  is  9°  C.  ;  for  tlie 
date,  15°  C  Bacterial  cultures  thrive,  likewise,  only  at  definite 
tcmj)eratures.  The  tubercle  bacillus  begins  to  grow  and  ])r()f)a- 
gate  at  2<S°  ('.  The  eHect  of  temperature  on  ciliary  movements 
can  readily  be  investigated  by  viewing  a  portion  of  the  mucous 
membrane  from  the  (esophagus  of  the  frog  under  the  ndcroscope, 
and  sul)jecting  to  warm  and  cold  saline  solutions.  A  glass  rod, 
healed  to  redness  and  brought  against  the  motor  nerve  of  a  frog's 
muscle,  will  produce  a  quick  contraction. 

There  are  in  existence  certain  vertebrates  (proteus)  in  which 
the  entire  skin  is  KciiKUive  to  light.  This  is  true  to  a  still  greater 
extent  of  the  onlinary  earth-worm.  ]>ut  among  the  higher  ani- 
mals the  end-organs  in  the  retina  are  alone  clearly  responsive  to 
jiliotic  stimii/dtloii.  It  has  been  found  that  when  the  skin  is  con- 
stantly ex])Osed  to  the  intense  light  of  the  electric  arc  lamp  that 
the  ephhelial  cells  of  the  skin  undergo  a  genuine  necrosis,  which 
is  not  brought  about  by  the  heat-rays,  but  by  the  short  waves  of 
the  violet  end  of  the  spectrum.  The  stimulating  power  of  light 
on  the  chlorophyll-containing  bodies  of  green  plants  is  easily 
shown  for  the  absorption  of  carbon  dioxide  and  the  formation  of 
starch  take  jilace  only  in  the  presence  of  light.  The  rhizojjod 
pelomvxa  responds  to  sudden  illumination  in  the  same  manner  as 
it  does  to  any  other  stimulus — namely,  by  quickly  taking  on  a 
spherical  form.  Certain  flagellate  and  ciliate  organisms  are  also 
so  sensitive  to  light  that  they  respond  by  quick  movements. 

The  excitation  effects  of  the  electrical  currents  have  been  inves- 
tigated most  throughly  in  nerve  and  muscle.  A  sudden  change 
in  the  intensity  of  a  current  arouses  a  nerve  impulse  in  the  nerve, 
and  calls  forth  a  contraction  of  the  muscle.  An  electrical  cur- 
rent, however,  stimidates  also  while  it  is  flowing  uninterru])t(Mlly 
through  any  living  structure.  This  is  shown  in  nerve  by  the 
heightened  irritability  at  the  kathode  or  region  where  the  current 
leaves  the  nerve  ;  in  actinospherium,  by  a  disintegration  of  the 
organism  at  the  region  of  the  anode,  where  the  current  enters  the 
structure  and  which  ceases  as  soon  as  the  current  is  interrupted. 
AmtTcba)  and   leucocytes   witlulraw  their   pseudopods  and    become 


32  GENERAL  INTRODUCTION. 

spherical  when  subjected  to  an  electrical  shock ;  smooth,  striated, 
and  cardiac  muscle  gives  vigorous  responsive  contractions  and  re- 
laxations ;  the  protoplasm  of  plant-cells  is  formed  into  spherical 
masses,  and  phosphorescent  animals  emit  light. 

The  inhibition  of  living  matter  is  much  more  difficult  to  recog- 
nize. A  chemical  inhibition  is  shown  by  the  action  of  anaesthetics. 
Mechanical  inhibition  has  been  demonstrated  by  several  investiga- 
tors by  showing  that  the  growth  of  bacteria  is  stopped  by  regular 
vibrations.  Heat  and  cold  will  both  produce  thermal  inhibition 
as  they  respectively  approach  the  coagulation-point  of  protoplasm 
and  the  zero-point.  There  is  no  indisputable  evidence  of  inhibi- 
tory power  of  light  (p/io^ic  inhibition).  The  changes  at  the  posi- 
tive electrode  when  a  current  is  passed  through  a  nerve  may  be 
regarded  as  an  example  of  inhibition  by  electricity. 

Cell  Tropism. — Organisms  that  are  capable  of  independent  loco- 
motion when  acted  upon  by  an  influence  coming  from  a  definite 
direction  move  either  toward  or  away  from  the  source  of  the  stim- 
ulus. If  the  latter  is  a  chemical  irritant,  the  phenomenon  is 
known  as  chemotropism  or  chemotaxis,  and  is  positive  or  negative 
according  as  the  animal  moves  toward  or  away  from  the  source 
of  the  stimulus.  In  like  manner,  pressure,  temperature,  light, 
and  electricity  produce  respectively  baro-,  thermo-,  helio-,  and  gal- 
vanotropism. 

The  Origin  of  Life. — It  may  be  said  that  as  long  as  the  earth 
was  a  molten  mass  of  excessively  high  temperature  life  could  not 
have  existed  as  we  know  it  to-day.  During  the  evolution  of  the 
earth  living  matter  must  have  arisen  as  the  result  of  physical  and 
chemical  factors,  as  all  chemical  compounds  whatsoever  have 
arisen.  The  formation  of  living  matter  was  as  necessarily  the 
product  of  evolution  as  was  the  formation  of  water.  At  first  it 
was  probably  capable  of  manifesting  vital  phenomena  indefinitely, 
which,  as  a  matter  of  fact,  is  true  of  germ-cells  at  the  present 
time.  Under  proper  circumstances  by  means  of  germ-plasm  life 
is  passed  from  individual  to  individual,  and  in  this  sense  cannot 
be  said  to  suffer  death. 

Cell  Death. — According  to  Weismann,  death  has  been  evolved 
for  the  good  of  the  species,  since  in  time,  through  wear  and  tear, 
the  vitality  of  aged  individuals  is  lessened  and  it  is  to  the  advan- 
tage of  the  species  that  such  individuals  should  no  longer  propa-. 
gate  nor  even  exist.     The  term  death  has,  however,  many  shades 


OENEUM.  isTi:<)i>r("rioy.  .T5 

of  nioaiiiiijr.  Ill  one  sense  since  living  matter  is  continually  iiii- 
<lci-goin<f  katal)()lic  changes.  It  is  continually  dying.  The  term 
Miav  he  applied  to  the  whole  organism  or  to  individual  tissues. 

Somatic  Death. — The  first  occurs  when  one  or  more  functions 
of  ihf  IkkIv  are  so  disturbed  that  harmonious  action  of  all  the  func- 
tions ])ecomes  inipo.^sihle.  The  most  convenient  sign  of  somatic 
death  is  the  cessation  of  the  heart-heat,  which,  however,  is  not 
always  the  cause  of  death.  The  deaih  of  (lie  tiimHes  does  not 
necessarily  take  place  with  somatic  death.  The  nervous  system 
dies  very  soon  ;  the  heart  lasts  longer,  the  last  portion  to  heat 
iteing  the  right  auricle.  The  smooth  muscle  of  the  intestines  re- 
mains irritable  for  three-quarters  of  an  hour,  and  striated  muscle 
at  times  for  hours. 

Some  of  the  most  ini[)ortaut  jjrohlems  of  general  physiology  are 
as  yet  highly  spiculative  in  character,  hut  most  physiologists  be- 
lieve that  as  knowledge  increases  they  will  all,  like  the  phenomena 
of  lifeless  bodies,  be  explained  as  the  result  of  the  properties  of 
matter  and  energy  working  under  definite  laws. 

QUESTIONS  OX  CHAPTER  I. 

Define  the  term  physiology. 
What  are  tlie  piinciiial  divisions  of  pliy.siology? 
What  is  meant  by  human  jihysioloi^y '/ 
(live  the  derivation  of  the  term  ])hysioh)gy. 
When  were  the  earliest  iihysioloftieal  ideas  lormed  ? 
Name  some  of  the  earliest  jihvsiologists. 

What  services  did  Calen.  Harvey,  Haller.  and  Miillei-  render? 
What  is  the  aim  or  ohjcct  of  |ihysiolo};y '.' 

How  is  it  possil)le  to  tell  whether  a  given  piece  of  matte  r  is  alive  or  not? 
What  are  the  fundamental  pro]K'rties  of  living  thinjis? 
Define  eaeh. 

Are  they  absolutely  characterLstic  of  living  matter? 
What  is  the  "physical  basis  of  life"? 
Describe  iirotopiasm. 

What  is  the  evidence  that  protoplasm  is  a  fluid? 
What  is  the  finer  structure  of  jirotoplasm? 
Why  is  protoplasm  not  a  chemical  term? 
What  substance  is  always  ])resent  in  i>rotoi>lasm  ? 
What  char.icterizes  the  elements  of  living  matter? 
What  is  a  cell? 

What  are  "histological  dilferentiation "  and  "  jiliysiological  division  of 
labor"  ? 

What  evidence  is  there  that  dead  protoplasm  ditl'ers  from  living? 

Descrilie  the  jiroperties  of  the  cyanogen  groii]>. 

What  is  a  biogen  ? 

What  are  metabolism,  anabolism.  and  katal>olisin? 

3— Phys. 


34  SECRETION. 

What  are  the  relations  of  anabolism  to  katabulism  during  rest,  gfowth,  and 
atrophy? 

Are  all  biogens  alike  ? 

Describe  the  internal  self-adjustment  of  metabolism. 

What  is  meant  by  "  contact  changes"  of  biogens? 

What  is  food? 

What  is  ingestion  ? 

What  are  enzymes  ? 

How  is  starch  formed  in  the  plant-cell  ? 

What  is  the  source  of  the  nitrogen  of  plants  ? 

What  is  the  function  of  the  nucleus  in  cells? 

Explain  why  reproduction  has  been  called  "  discontinuous  growth," 

What  is  growth  due  to  ?     Effect  of  exercise  ? 

Give  the  various  stages  of  growth. 

Describe  both  methods  of  cell-division. 

What  two  methods  of  reproduction,  and  how  do  they  differ? 

Describe  conjugation. 

How  do  male  and  female  germ-cells  differ? 

What  is  fertilization  ? 

What  is  parthenogenesis  ? 

What  is  the  object  of  fertilization? 

What  forces  are  active  during  the  development  of  the  ovum? 

What  is  atavism  or  reversion  ? 

Discuss  the  inheritance  of  acquired  characters. 

What  is  the  source  of  germ-plasm  ? 

What  is  meant  by  preformation  and  epigenesis? 

What  are  variations  of  germ-plasm  due  to  ? 

What  is  natural  selection  ? 

Define  phylogeny  and  ontogeny. 

What  opposite  results  may  stimuli  produce  in  living  matter? 

How  may  stimuli  produce  necrobiotic  changes? 

Give  examples  of  excitation  and  inhibition  of  active  protoj)lasra. 

Define  positive  and  negative  chemotropism. 

What  can  be  said  of  the  origin  of  life  ? 

Give  various  meanings  of  the  term  death. 

What  is  the  cause  of  somatic  death  ? 


CHAPTER    11. 

SECEETION. 


The  term  secretion  may  be  used  to  designate  either  the  liquid 
or  semiliquid  products  of  glandular  organs  which  are  discharged 
upon  free  or  closed  surfaces ;  or  to  designate  the  process  itself  by 
which  these  products  are  formed.  According  as  the  surface  is  free 
(skin,  mucous  membrane)  or  closed  (blood  and  lymph  cavities) 


tlic  socrction  is  (cruu'd  an  cxlcnittl  or  an  inliriKil  sccrdioii.  Siidi 
siihstaiici'S  s(^rviiig  a  useful  purpose  are  ti/piraJ  .srrntioiix  ;  when  ol" 
IK)  tiirtlier  use,  are  excirtiouH.  There  is  no  longer  any  (loul)t  that 
i/fiiiid-crf/s  arc  artive  in  (lie  fonnnlion  of  tlirlr  Hccniloiis.  The 
proois  are  : 

1.  The  irlaiul-cells  undergo  a  niicroscopical  ehange. 

2.  Spccitic  sulislanccs  in  the  secrt'tion  which  are  not  found  in 
llic  lilood  or  Ivniph. 

•  ">.  The  liheration  of  eneriry  in  the  form  of  heat,  pressure,  and 
electricity. 

4,  The  results  of  the  stinuilatiou  of  the  nerve-supply. 

5.  The  action  of  certain  <lrugs. 

The  jjrocesses  of  fi/fratloii,  (liff^iision,  and  0!<mosi'<  cannot,  how- 
ever, he  entirely  excluded  for  acting  in  conjunction  with  the 
]>hysical  and  chemical  properties  of  the  living  structure  of  gland- 
cells.  By  fi/lnifion  is  meant  the  passage  of  tluids  through  a 
mcmhrane  as  the  result  of  differencas  of  hydrostatic  pressure. 
Dllf'i(!iio)i  is  the  interpenet ration  of  the  molecules  of  two  tluids 
when  hrought  into  contact.  Osmosis  or  dialysis  is  the  diffusion 
that  takes  place  through  membranes  separating  two  fluids. 

SALIVARY  GLANDS. 

The  production  of  saliva  is  brought  about  by  the  joint  action  of 
thre(^  larger  pairs  of  glands,  the  parotids,  fdihrndxi/larirs,  and  su/h 
lliH/}(((/s,  and  by  iitnnmerablr  sma/lrr  ones  lying  in  the  mucous  mem- 
brane of  the  mouth  and  tongue.  In  close  proximity  to  the  jiarotid 
lies  a  glandular  mass  called  by  Klein  the  inferior  admaxiUarri 
(socia  jHtrotidis  of  man),  and  in  the  connection  with  the  sublingual 
is  a  separable  portion,  the  superior  admaxiUary.  These,  as  well 
as  many  unicellular  glands,  pour  their  secretions  into  the  buccal 
cavity. 

The  distinction  lietween  nlbiiminous  and  mucous  (jldixla  becomes 
definite  oidy  when  applied  to  individual  cells.  A  series  of  glands 
might  be  gathered,  showing  every  gradation  from  those  entirelv 
mucous  to  those  entirely  albuminous.  The  demilunes  of  Heiden- 
hain  in  mucous  glands  are  albuminous  cells.  The  two  types  of 
cells  differ  not  only  histologically,  but  also  in  the  character  of 
their  products.  The  secretion  from  albuminous  cells  contains, 
iicsides  enzytnes,  water,  salts,  and  alitumin.  while  that  from  miieona 
C''//>' contains  mucin,  which  niaUcs  it  striiiirv  and  viscid. 


36 


SECRETION. 


The  activity  of  secretory  cells  is  well  shown  by  the  salivary 
glands.  During  secretion  the  granules  which  are  present  gradu- 
ally disappear  from  the  outer  side  of  the  cells,  and  a  clear  non- 


FiG.  3. 


v.sym 


V.J. 

nfi.sym.sm 


r.sm.p.        v.sm. 


Diagrammatic  representation  of  the  submaxillary  eland  of  the  do,?,  with  its 
nerves  and  blood-vessels.  The  dissection  has  been  on  an  animal  lying  on  its  back, 
but  since  all  the  parts  shown  in  the  figure  cannot  be  seen  from  any  one  point  of 
view,  the  figure  does  not  give  the  exact  anatomical  relations  of  the  several  struc- 
tures (Foster). 

sm.gld.  The  submaxillary  gland,  into  the  duet  (sm.  d.)  of  which  a  canula  has 
been  tied.  The  sublingual  gland  and  duct  are  not  shown.  n.L,  n.V .  The  lingual 
branch  of  the  fifth  nerve  ;  the  part  n.l.  is  going  to  the  tongue,  ch.t,  ch.t'.,  rht".  The 
chorda  tympani.  The  part  ch.t".  is  proceeding  from  the  facial  nerve :  at  ch.t'.  it 
becomes  conjoined  with  the  lingual  n.l'.,  and  afterward  diverging,  passes  as  rh.t.  to 
the  gland  along  the  duct;  the  continuation  of  the  nerve  in  company  with  the  lin- 
gual n.l.  is  not  shown.  .«?w.  fjl.  The  submaxillary  ganglion  with  its  several  roots. 
n.  car.  The  carotid  artery,  two  small  branches  of  which,  o.  sm,.  n.  and  r.  sm.  p..  pass 
to  the  anterior  and  posterior  parts  of  the  gland,  r.  sm.  The  anterior  and  posterior 
veins  from  the  gland,  falling  into  v..j.,  the  jugular  vein.  ?>.  sym.  The  conjoined  vagus 
and  sympathetic  trunks,  rj.  rer.  s.  The  upper  cervical  ganglion,  two  branches  of 
which,  forming  a  plexus  {n.  f.)  over  the  facial  artery,  are  distributed  fn.  sym..  sm  ) 
along  the  two  glandular  arteries  to  the  anterior  and  posterior  portions  of  the  gland. 

The  arrows  indicate  the  direction  taken  by  the  nervous  impulses  during  reflex 
stimulation  of  the  arland.  They  ascend  to  the  brain  by  the  lingual  and  descend  by 
the  chorda  tympani. 


stainable  material  is  substituted.  The  nuclei  become  more  spheri- 
cal and  lie  nearer  the  centre  of  the  cell-body,  which  shrinks  in 
size.     The  granular  material  is  apparently  used  up  in  the  forma- 


SAiJVAnv  (;L.\.\ns.  37 

tion  iif"  llic  sccn'tioii,  and  since  tlic  ciizyuK'.s  iorinod  arc  ppccilic 
Milislaiici'S,  tlic  lormcr  arc  taken  to  l»c  tli«'ir  source  and  desi^Miatcd 
as  ziivKKjen  (jniiiitlis.  The  forerunner  oi' ptijaliii  i.s  called  ptya/ino- 
(jni  ;  of  jnjtsiii,  /iiji>iiiiu(/eii,  etc. 

The.  pre  SSI  I  rr  in  the  duct  of  the  submaxillary  has  been  observed 
at  1!M)  nun.  Hi;,  while  the  blood  pressure  in  the  carotid  at  the 
liiiK'  was  but  112  mm.  Hg.  The  question  of  the  amount  of  heat 
trivi'u  otrdurini;  the  activity  of  the  <rland  is  still  unsettled.  Lud- 
wiir  and  Spiess  oriizinaily  determined  the  saliva  to  be  1°  warmer 
than  the  bhtod  in  the  carotid.  Ilcideidiain,  by  the  thermo-electric 
method,  found  the  diHerence  to  become  greater  on  stimulation  of 
the  sym[)athetic.  The  rlectrical  changes  in  glands  are  analogous 
to  the  action  currents  iu  muscles.  The  current  may  be  ingoing, 
outgoing,  or  diphasic  in  character. 

Nervous  Factors. — The  salivary  glands  have  a  cranial  and  a 
symjiitUirtic  iierve-supj)ly,  whose  influence  may  be  illustrated  by 
the  results  obtained  from  the  submaxillary  of  the  dog.  When 
the  rhonla  tipnjiaHi,  whose  fibres  are  cranial  in  orgin,  is  stimulated 
with  weak  induction  shocks,  the  saliva  obtained  is  relatively 
abundant,  thin,  aud  watery,  containing  not  more  than  1  to  2  per 
cent,  of  solids.  The  gland  becomes  redder  in  color,  the  veins  are 
distended,  and  the  blood  sliows  a  distinct  pulse,  indicating  a  dila- 
tation of  the  small  arteries  and  that  the  chorda  tympani  carries 
dilator  fibres.  Stimulation  of  the  symjiaihetk  fibres  produces  a 
scanty  secretion,  which  is  thick  and  turbid  and  may  contain  6  per 
cent,  of  solids.  The  gland  becomes  paler,  the  blood  flow  is  les- 
sened, showing  that  a  vasoconstriction  has  occurred. 

Circulatory  Factors. — That  the  character  of  the  secretion  is  not 
entirely  due  to  the  changes  in  the  amount  of  blood  flowing  to  the 
glands  is  shown  l)v  the  following  facts : 

1.  The  blood-flow  may  be  cut  off  entirely  when  stimulation  of 
the  chorda  tymjiani  still  gives  a  secretion. 

2.  Injection  of  atrojiine  ]»roduces  an  increased  flow  of  blood, 
but  no  secretion  upon  stimulation  of  the  chorda. 

3.  Injection  of  hydrochlorate  of  quinine  gives  a  vascular  dila- 
tation, but  no  secretion  until  the  nerve  is  stimulated. 

When  the  chorda  is  irritated  with  shocks  of  increasing  intensity, 
it  is  found  tiiat  the  amount  of  water  and  .salts  secreted  increases 
projiortionately  to  a  maximum  limit,  which  for  salts  is  about  0.77 
per  cent.,  no  matter  what  the  condition  of  the  gland  mav  be.     The 


38  SECRETION. 

production  of  organic  constituents  soon  reaches  a  maximum  and 
then  declines,  and  is  closely  dependent  upon  the  previous  condition 
of  the  gland.  In  order  to  explain  these  facts  Heidenhain  decided 
that  there  were  two  sets  of  nerve-fibres,  one  of  which  regulated  the 
formation  of  organic  substances  {trophiG  fibres),  and  the  other  of 
which  regulated  the  production  of  water  and  salts  {secretory  fibres). 
Moreover,  their  arrangement  was  such  that  the  chorda  carried  a 
greater  number  of  secretory,  while  the  sympathetic  carried  more 
trophic  fibres.  Langley  has  recently  offered  a  simpler  explanation 
of  the  facts,  attributing  the  differences  of  the  chorda  and  the  sympa- 
thetic saliva  to  the  variations  in  the  quantity  of  blood  supplied,  so 
that  the  assumption  of  only  one  kind  of  nerve-fibre  is  necessary. 

Section  of  the  chorda  tympani  produces  after  a  few  days  a  slow, 
continuous  secretion  for  five  or  more  weeks,  when  it  ceases.  This 
is  called  paralytic  secretion.  Antilytic  secretion  is  the  production 
of  a  flow  by  the  corresponding  gland  on  the  opposite  side,  the 
nerves  of  which  are  still  intact.  Section  of  the  cervical  sympathetic 
causes  a  temporary  dilatation  of  the  blood-vessels,  but  has  no  other 
effect.  Atropine  prevents  the  secretion  of  saliva  by  destroying 
the  endings  of  the  cerebral  fibres  in  the  gland,  leaving,  when 
proper  doses  are  used,  the  sympathetic  fibres  still  capable  of  func- 
tioning. Pilocarpine  has  an  antagonistic  action  to  atropine,  causing 
a  continual  secretion  by  stimulating  the  cerebral  fibres  in  the 
gland.  Nicotine  causes  a  slight  flow  of  saliva,  followed  by  a  par- 
alysis. The  drug  acts  upon  the  end-brushes  of  both  the  cranial 
and  sympathetic  fibres  in  the  superior  cervical  and  submaxillary 
ganglia. 

Mechanism  of  Saliva  Secretion. — The  flow  of  saliva  is  normally 
a  reflex,  the  afferent  impulses  passing  along  the  glossopharyngeal 
and  lingual  nerves  to  the  centre  in  the  medulla,  which  lies  near 
the  nuclei  of  origin  of  the  seventh  and  ninth  nerves.  The  efferent 
path  is  for  the  submaxillary  gland  along  the  facial,  chorda  tympani, 
and  lingual  nerves.  The  secretion  may  be  called  out  by  the 
stimulation  of  many  sensory  nerves,  sciatic,  splanchnic,  and  vagus, 
as  well  as  by  psychical  states  as  the  thought  of  food  or  in  nausea. 
Fear  and  embarrassment  may  inhibit  the  flow. 

STOMACH. 
Gastric  Glands. — Two  kinds  of  cells  are  present  in  the  gastric 
glands,  known  as  chief  cells  and  border  cells.     The  former  are 


sn  )M.\<'U-^i'.\  \f  v:  /•;.  i  .v.  ;?n 

alone  present  in  the  jit/loric  end  of  the  stomach,  ami  it  has  been 
stated  l)y  Ileideiihain  that  this  |)ortiou  of  the  stomach  produces  no 
acid.  The  jnjlorie  end,  cartj'ulbj  rejected  and  converted  into  a  blind 
pourli,  isitlkaline  in  reaction.  This,  by  exclusion,  leaves  the  border- 
cells  a:5  the  sonrre  of  the  hi/<lri>rliloric  ariil  of  the  gastric  juice. 
During  the  activity  of  the  i^astric  irlaiids  liistoioLrical  changes  take 
place  especially  in  the  chief  colls,  similar  to  those  already  de.-^cribeil 
in  the  salivary  glands.  They  also  have  a  double  supply  of  cranial 
and  si/nijiatltetic  nerves.  ^Stimulation  of  the  vagi  after  a  latent 
|)eriod  of  from  four  and  one-half  to  ten  minutes  gives  a  distind 
How.  The  delay  is  due  to  the  simultiineous  irritiitiou  of  inhibitory 
fibres.  Stimulation  of  the  sympathetic  gives  no  result.  The 
etiect  of  psvchical  states  is  shown  in  the  "fictitious  lueal  "  experi- 
ment, in  which  the  a'sophagus  of  a  dog  is  divided  and  the  two 
ends  are  brought  to  the  skin  and  sutured  so  as  to  open  externally. 
Food  taken  by  the  dog  does  not  reach  the  stomach,  but  neverthe- 
le.^^s  causes  a  How  of  gastric  juice,  which  has  been  shown  to  depend 
u\)Oii  the  integrity  of  the  vagi.  The  sight  of  food  is  alone  suffi- 
cient to  cause  a  secretion.  lu  order  to  determine  the  mechanism 
of  the  normal  secretion  of  the  gastric  juice  investigators  have 
converted  a  part  of  the  fundus  of  the  stomach  into  a  blind  pouch 
with  an  external  opening,  while  the  continuity  of  the  stomach  was 
established  by  uniting  tlu-  cut  ends.  The  nerve-sup])ly  was  not 
destroyed.  The  introduction  of  food  into  the  stomach  brought 
out  a  secretion  in  the  resected  portion  in  from  fifteen  to  thirty 
minutes.  This  was  interpreted  to  be  due  to  the  absorption  of 
digested  substances  from  the  stomach.  The  quantity  of  the  gastric 
juice  secrete<l  varies  with  the  amount  of  food  to  be  digested, 
while  the  quality  de]>ends  upon  the  character  of  the  food.  There 
is  no  evidence  that  the  cells  of  the  gastric  glands  can  be  stimulated 
directly.  The  How  upon  me<"hanical  stimulation  is  effected  through 
the  fibres  of  the  vagus  and  possibly  of  the  sympathetic. 

PANCREAS. 

The  cells  of  the  pancreas  are  mainly  of  the  albinninnns  ttjpe,  in 
additi(m  to  which  irregular  masses  of  cells  (bodies  of  Langerhans) 
are  to  be  found.  The  latter  are  clear  an<l  small,  with  readily 
slainable  nuclei.  The  others  show  a  clear,  well-<lelint'(l,  non-stain- 
able  zone  toward  the  lumen.     During  activitv  the  cell-boundaries 


40  SECRETION. 

become  more  distinct  and  the  granular  zone  becomes  narrower. 
Stimulation  of  the  medulla  increases  the  flow  of  the  pancreatic 
juice  and  changes  its  organic  constituents.  There  are  present 
secretory  nerves  comparable  to  those  of  the  salivary  glands. 
Owing  to  the  sensitiveness  of  the  gland  to  variations  in  the  blood- 
supply  stimulation  of  the  sympathetic  will  result  in  a  flow  of  secre- 
tion only  if  the  vasoconstrictor  fibres  are  allowed  to  degenerate  by 
previous  section.  Stimulation  of  the  vagus  also  causes  a  marked 
secretion,  both  cases  requiring  a  long  laient  period,  due  probably 
to  simultaneous  stimulation  of  inhibitory  fibres.  The  normal 
secretion  of  the  pancreatic  juice  begins  very  soon  after  the  inges- 
tion of  food  into  the  stomach,  and  is  due  to  a  reflex  stimulus  from 
the  mucous  membrane  of  the  stomach  and  duodenum  resulting 
from  the  acidity  of  the  gastric  juice.  A  relation  has  been  shown 
to  exist  between  the  quantity  and  quality  of  the  pancreatic  secre- 
tion and  the  nature  of  the  food. 

LIVER. 

The  amount  of  bile  secreted  varies,  but  for  man  may  be  stated 
to  be  about  800  c.c.  a  day.  The  liver-cells  which  are  in  relation 
to  the  mixed  blood  of  the  portal  vein  and  the  arterial  blood  of 
the  hepatic  artery  are  probably  continuously  active.  The  bile, 
stored  in  the  gall-bladder,  is  ejected  intermittently.  It  has  been 
shown  that  the  quantity  of  bile  formed  varies  with  the  quan- 
tity and  quality  of  the  blood  supplied  to  the  liver.  Bile-salts 
stimulate  liver-cells,  and  all  such  substances  are  designated  as 
cholagogues. 

Stimulation  of  the  spinal  cord,  diminishes  the  secretion,  owing 
to  constriction  of  the  blood-vessels  of  the  abdominal  organs.  Sec- 
tion of  the  cord  resulting  in  loss  of  vascular  tone  and  general  fall 
of  blood  pressure,  and  velocity  decreases  the  secretion.  Stimula- 
tion of  the  splanchnics  which  have  been  cut  diminishes  secretion, 
owing  to  vascular  constriction  of  the  abdominal  organs,  while  sec- 
tioning alone  increases  the  secretion,  since  the  resulting  loss  of 
vascular  tone  is  limited  to  the  abdomen,  resulting  in  a  greater 
flow  of  blood  to  that  region.  The  determination  of  distinct  secre- 
tory fibres  for  the  formation  of  bile  has  so  far  been  impossible. 
In  jaundice  due  to  the  occlusion  of  the  bile-ducts  the  bile  is  not 
reabsorbed  by  the  blood  directly,  but  by  the  lymphatics  of  the 
liver,  and  gets  into  the  blood  through  the  thoracic  duct. 


lyTh'srix.  I  /,  <;  l.  i  .\7>.s-  kidsf.  y.  41 

INTESTINAL  GLANDS. 

Evidence  as  a  whole  poiiilii  to  tlu-  la<t  thai  many  cells  of  the 
intestinal  jjlands  under^'o  hisitolof^ical  chan^'es  durini;  activity,  in 
that  tlu'ir  ir  ran  tiles  disa|)|H'ar.  Srciiim  of  iiitr.'<tiiia{  nfrir.i  so  that 
the  hiu'lier  centres  are  separated  from  the  nuicons  nieinhrane  lea<ls 
to  an  aeewniidation  of  lliiid  ;  hnt  if  the  iiij'>  rior  (/niKjlioii  of  the  solar 
plcxiia  it}  left  intact,  the  actniniulation  does  not  take  place. 

SEROUS  SECRETIONS. 

These  are  produced  by  the  pleura,  peritoneum,  tuni<"i  vairi- 
nalis,  and  by  the  synovial  membranes  of  joints,  tendon-sheath.s, 
etc.  The  synovial  secretion  is  more  glairy  and  viscid  than  is  truly 
serous  secretion,  which  is  very  much  like  lymph.  The  function 
of  serous  secretion  is  to  prevent  friction  between  surfaces  that  are 
in  contact.  It  is  of  a  pale  yellow  color,  alkaline  in  reaction, 
viscid,  and  coagulable  by  heat. 

LACHRYMAL  GLANDS. 

The  conclusion  reacheil  for  the  salivary  glands  may  be  applied 
with  little  alteration  to  the  glands  of  the  na.sal  mucous  mem- 
brane and  to  the  lachrymal  glands.  The  latter  resemble  an 
alliuminous  .salivary  gland,  receiving  cranial  secretory  fibres  by 
way  of  the  fifth  nerve,  and  ■■o/mjxdlictic  fibres  by  way  of  the 
cervical  .sympathetic.  .Stimulation  of  most  sensory  nerves  pro- 
duces a  secretion  reflexly.  The  ducts  of  the  gland  lead  to  the 
conjunctiva  of  the  upper  eyelid,  and  usually  the  secretion  is  just 
sutficient  to  keep  the  eye  moi.st,  and  is  drained  into  the  nasal 
cavity  by  way  of  the  lachrymal  duct.  When  the  secretion  is 
formed  in  superabundance,  it  ap|)ears  as  fears.  The.se  are  alka- 
line in  reaction  and  contain  1  per  cent,  of  solids,  chiefly  chloride 
of  soilium. 

KIDNEY. 

Although  tiie  kidney  is  ric-hly  supplied  with  nerves,  there  is  no 
iiulisputable  evidence  of  secretory  fibres,  but  changes  in  the  secre- 
tion of  urine  can  be  explained  by  variations  in  the  blood-tlow.  It 
has  been  estimated  that  the  supply  of  blood  to  the  kidney  n)ay  be 
from  four  to  nineteen  times  as  large  as  that  of  (»ther  organs  of 
the  body,  and  equals  per  minute  o.G  per  cent,  of  the  total  cpiantity 


42  SECRETION. 

seut  out  by  the  left  heart.  The  secretion  of  urine  can  be  measured 
directly,  but  variations  in  blood-supply  are  determined  by  an  in- 
strument called  an  oncometer.  A  rich  supply  of  vasoconstrictor 
hbres  for  the  kidney  emerge  from  the  cord  in  the  lower  thoracic 
spinal  nerves  (dog),  pass  through  the  sympathetic  system,  and 
reach  the  kidney  as  non-medullated  nerves.  Stimulation  of  these 
nerves  causes  a  shrinkage  of  the  organ  and  a  diminution  of  the 
secretion.  When  the  fibres  are  cut,  the  arteries  dilate,  the  organ 
enlarges,  more  blood  passes  through  the  kidney,  and  the  secretion 
is  augmented.  The  vasodilator  fibres  to  the  kidney  emerge  from 
the  cord  through  the  anterior  roots  of  the  eleventh,  twelfth,  and 
thirteenth  spinal  nerves.  Normally  these  fibres — i.  e.,  constrictor's 
and  dilators — are  brought  into  activity  reflexly  and  regulate  the 
formation  of  the  secretion.  Any  factor  that  increases  the  differ- 
ence in  pressure  in  the  renal  artery  and  the  renal  vein  will  cause 
increased  secretion  of  urine.  Vascular  dilatation  of  the  vessels 
of  the  kidney,  unless  counterbalanced  by  a  general  fall  of  blood- 
pressure,  will  give  an  increased  secretion.  The  following  table  is 
useful  for  reference : 


Table    of  the  Relation  of  the   Secretiox  of   Urine   to   Arterial 
Pressure  (Kirke). 

A.   Secretion  of  urine  may  be  increased — 

(a)  By  increasing  the  general  blood-pressure  by — 

1 .  Increase  of  the  force  or  frequency  of  the  heart-beats. 

2.  Constriction  of  the  small  arteries  of  areas  other  than  that 

of  the  kidney. 
{b)  By  increasing  the  local  blood-pressure  by  relaxation  of  the  renal 
artery,  without  compensating  relaxation  elseiohere  by — 

1.  Division  of  the  renal  nerves  (causing  polyuria). 

2.  Division  of  the  renal  nerves   and   stimulation  of  the   cord 

below  the  medulla  (causing  greater  polyuria). 

3.  Division  of  the  splanchnic  nerves  ;  but  the  polyuria  is  less 

than  in  1  or  2,  as  these  nerves  are  distributed  to  a  wider 
area,  and  the  dilatation  of  the  renal  artery  is  accompanied 
by  dilatation  of  other  vessels,  and  therefore  by  a  some- 
Avhat  general  increase  of  blood-supply. 

4.  Puncture  of  the  floor  of  the  fourth  ventricle  or  mechanical 

irritation  of  the  superior  cervical  ganglion  of  the  sym- 
pathetic, possibly  from  the  production  of  dilatation  of  the 
renal  arteries. 


h'in.\i:y.  43 

//.    Sri'retinn  i>f  tin'  urine  viai/  lie  iliniiiiis/inl — 

{a)    liij  diniiiiisluiiij  l/ir  i/iiicriil  bfoinl-pifssurc  />i/ — 

1.    IMiiiiimtion  of  tlif  torro  or  rrf(|U('iuy  df  tlio  lioart-ln'Jit.s. 
l:.    l>ilatati()ii  of  rapillary  aiTus  titlicr  iliaii   that  of  tin-  kiiliiry. 
;>.    division  of  tlic  .-iiiiiial  cord  Ijcltiw  tlu'  medulla,  wliirli  cuuscs 
a  dilatation  of  tin'  irciifral  alidominal  area,  ami  uriiic  ^CK- 
crally  i-oasos  hcin^  sciTctcd. 
(//)    /{i/  inrrai.siiKj  titf  blood-firvssure  by  stiimilatioii   of  the  spinul 
coril  ht'low  the  iiiodulla.  the  constrietioii  of  the  renal  artery 
which   riillows  not  iicinir  compensated   for  hy  the  increase 
of  jicneral  Mood-pressure. 
((•)  By  cons/iicfi(in  of  the  rciuil  aifcri/  l)y  !stimulatin<r  the  renal  or 
splanchnic  nerves  or  the  spinal  cord. 

Ludwic:  resrariled  the  pecretiou  of  urine  as  due  to  simple  filtra- 
tion and  osmosis  taking  place  in  the  glomeruli,  and  to  a  coneentra- 
tiou  in  the  convolute<l  tuhules  ol'  the  fluid  thus  formed.  Recent 
work  has  shown  that  the  cells  of  the  convoluted  tubes  have  a  dis- 
tinct secretory  function  in  the  elimination  of  urea  and  related 
bodie.*!.     The  evitlence  is  : 

1.  lu  birds,  where  uric  acid  takes  the  place  of  the  urea  of  mam- 
mals, the  small  solubility  of  the  urates  enables  experimeuters,  by 
ligation  of  the  ureters,  to  cau.^e  a  deposit  which  is  always  found  in 
the  cells  of  the  convoluted  tid)es. 

2.  Indigo-carmine  injected  into  the  circulation  of  a  living 
animal  may  be  precipitated  by  the  injection  of  alcohol,  when  the 
pigment  is  always  fomid  in  the  convoluted  tubes. 

.S.  The  inactive  cells  of  the  convoluted  tubes  are  snuill,  granu- 
lar, and  toward  the  lumen  show  a  striated  border.  During 
activity^  they  lose  their  striated  border,  project  into  the  lumen  of 
the  tubule,  making  it  smaller,  and  a  clear  vesicular  area  is  formed 
near  the  nucleus.  The  vesicle  ruptures  and  empties  its  contents 
into  the  lumen. 

The  excretion  of  water  and  salts  takes  ])lace  mainly  through 
the  glomeridar  epithelium.  There  are  no  secretory  nerves.  Sec- 
tion of  the  cord  in  the  cervical  region,  which  results  in  a  general 
fall  of  blood-pre.<sure.  diminishes  the  secretion.  In  general  it  has 
been  found  that  the  .secretion  of  urine  varies  both  with  the  pressure 
of  the  blood  in  the  glomeruli  and  the  quantity  of  blood  flowing 
through  the  kidney,  and  Heidenhain  has  insisteil  upon  the  latter 
factor  as  the  essential  one,  giving  as  evidence  the  fact  that  com- 
pression of  the  renal  vein  sto(»s  tiie  Mow  ol'the  mini'.      This  raises 


44  SECRETION. 

the  pressure  in  the  glomerulus,  but  stops  the  flow  of  blood.  Liga- 
tion of  the  vein  for  one-half  minute  will  stop  the  secretion  for 
three-quarters  of  an  hour,  so  that  it  probably  depends  upon  the 
living  structure  of  the  epithelial  cells.  The  action  of  substances, 
like  potassium  nitrate,  which  increase  the  flow  of  urine  and  are 
known  as  diuretics,  is  explainable  in  two  ways : 

1.  They  may  cause  hydrsemic  plethora  by  drawing  water  from 
the  tissues,  thus  increasing  the  blood-pressure  and  favoring  filtra- 
tion. 

2.  The  substances  may  act  directly  upon  the  cells  of  the  glom- 
eruli. 

Abnormal  constituents  of  the  urine  in  disease,  as  albumin  in 
nephritis  or  sugar  in  diabetes,  escape  from  the  blood  through  the 
glomerular  epithelium.  Urea  in  the  blood  acts  as  a  stimulus  to 
the  cells  of  the  convoluted  tubules,  causing  its  selection  from  the 
blood  where  its  percentage  is  less  and  its  excretion  into  the  tubules 
where  its  percentage  is  greater. 

URINE. 

The  urine  is  a  clear,  yellowish  liquid,  of  a  slightly  acid  reaction, 
a  characteristic  odor,  salty-bitter  taste,  and  an  average  specific 
gravity  of  1017  to  1020.  The  daily  amount  formed  may  be 
placed  at  from  1200  to  1700  c.c.  The  color  is  due  to  a  pigment, 
urobilin,  derived  from  the  bilirubin  of  the  bile,  and  its  various 
tints  are  due  to  various  stages  of  oxidation.  The  acidity,  which 
is  due  to  acid  sodium  and  acid  calcium  phosphate,  is  less  during 
active  digestion,  particularly  of  vegetable  foods.  Herbivora  have 
alkaline  urine  except  during  starvation.  That  there  is  no  free 
acid  present  is  shown  by  the  fact  that  no  precipitate  is  formed  upon 
the  addition  of  sodium  hyposulphite.  tJpon  standing  fermenta- 
tion usually  results,  due  to  the  presence  of  bacteria,  which  causes 
first  a  precipitate  of  uric  acid  and  urates  and  later  of  triple  phos- 
phates. The  urine  is  very  complex,  because  the  kidneys  eliminate 
not  only  the  normal  end-products  of  metabolism,  with  the  excep- 
tion of  carbon  dioxide,  but  also  products  of  decomposition  from 
the  alimentary  canal  and  substances,  like  drugs,  that  are  not 
ordinarily  regarded  as  foods.  A  useful  rule  for  approximately 
estimating  the  total  solids  in  any  given  specimen  of  healthy  urine  is 
to  multiply  the  last  two  figures  representing  the  specific  gravity  by 


ri'jsK.  15 

•ji.-i'i.  Thus,  in  urine  i»f  a  spccilic  <;ravi(y  of  102"),  'io  tinics  2.;>.'> 
equals  aiS/if)  iri-;iiiis  111'  solids  in  1000  cc.  of  urine.  In  usin;^ 
this  iiirlluxl  it  must  ho  reinenihered  tiial  tiie  liniils  of  error  are 
nuieh  widi'r  in  diseased  than  in  healthy  urine. 

The  most  ini|)ortaut  constituents  of  the  urine  are  urea,  nric 
arid,  .ranfliiii,  lni/i(i.rant}iiii,  gvanin,  adniiii,  rrratiiiln,  hippitnc 
acid,  coiijiujdtcd  .'<i(lj)li(t()'s,  uater,  and  xalf.^. 

Urea,  an  amide  of  earhonie  ueid,  is  found  in  rehitively  larjre 
quantities  (2  per  eent.  or  morej.  Twenty -four  hours'  urine  con- 
tains from  ."^O  to  o4  grammes.  It  is  the  end-produet  of  the  ]>hy- 
sioioi,neal  oxidation  of  j)roti'ids  and  albuminoids.  One  gramme  of 
proteids  yiehls  ;■  of  a  gramme  of  urea,  as  determined  from  the  con- 
tained nitrogen.  But  as  some  nitrogen  is  eliminated  iu  uric  acid, 
ereatiuin,  etc.,  the  amount  of  urea  cannot  he  ttiken  as  an  indica- 
tion of  the  total  i)roteid  hroken  down.  Urea  is  also  found  in 
other  secretions,  as  the  milk  and  the  perspiration. 

The  kidnev  does  not  manufacture  urea,  as  is  shown  hv  these 
focts : 

1.  I'rea  does  not  form  in  the  l)lood  when  irrigated  tlirougli  an 
isolated  kidney. 

2.  The  urea  in  the  hlood  (0.03  to  0.15  per  cent.)  accumulates 
steadily  as  long  as  the  animal  lives  if  the  kidneys  are  extirpated. 

The  evidence  that  urea  is  formed  in  the  liver  is  as  follows : 

1.  The  hlood  of  a  well-fed  dog,  when  irrigated  through  an  iso- 
lated liver,  increases  in  the  amount  of  urea  contained,  which  is  not 
true  of  the  hlood  of  a  fasting  animal,  from  which  jnay  he  concluded 
that  the  first  contains  sul)Stances  which  the  liver  can  convert  into 
urea. 

2.  This  power  is  })ossessed  only  hy  the  liver. 

3.  Ammonium  carhonate  added  to  the  blood  and  irrigated 
through  the  liver  is  converted,  at  least  partially,  into  urea. 

4.  Removal  of  the  liver  decreases  the  percentage  of  urea  in  the 
blood. 

Trea  arises  from  ])roteids  by  hydrolysis  and  oxidation  with  the 
formation  of  ammonia  compounds,  which  are  changed  to  urea  in 
the  liver.  Ammonium  carbamate  may  he  one  of  the  precursors 
of  urea,  having  been  found  in  the  hlood  of  dogs,  and  is  easily 
converted  into  urea  by  the  loss  of  water.  However,  other  and 
more  complex  anmionia  conijiounds,  like  leucin  and  glycocoll,  can 
be  converted  into  urea  hy  tln'  liver.      Tiie  hlood  of  the  ])ortal  vein 


46  SECRETION. 

is  normally  three  or  four  times  as  rich  in  anniionia  compounds  as 
is  arterial  blood.  Since  ured  does  not  entirely  disappear  upon 
extirpation  of  the  liver,  it  must  have  some  other  source,  and  a 
decomposition-product  of  proteid  by  trypsin — lysatinin — has  been 
suggested  as  a  possible  source. 

Uric  Acid. — Its  total  quantity  in  the  urine  in  twenty-four  hours 
varies  from  0.2  to  1  gramme.  In  birds  and  reptiles  it  takes  the 
place  of  urea  as  the  main  end-product  of  the  disintegration  of 
proteids,  and  its  place  of  origin  has  been  proved  to  be  the  liver. 
In  mammals  this  has  not  been  substantiated.  According  to  one 
investigator,  uric  acid  is  derived  from  nucleins  being  their  specific 
end-products :  for,  among  other  things,  it  is  found  that  feeding 
with  substances  rich  in  nucleins,  like  the  thymus  gland,  leads  to 
an  increased  elimination  of  uric  acid.  Upon  feeding  an  animal 
with  uric  acid  it  is  found  that  some  of  it  is  excreted  as  urea. 

Xanthin,  hypoxanthin,  guanin,  adenin,  etc.,  which  are  closely 
related  to  uric  acid,  are  probably  derived  from  the  same  source. 
They  are  found  in  the  greatest  quantity  in  muscle. 

Creatinin  is  derived  partly  from  proteids  eaten  and  partly  from 
the  metabolism  of  proteids  in  the  body.  Muscle  contains  creatin 
as  a  constant  constituent,  which,  when  taken  into  the  stomach,  is 
eliminated  as  creatinin,  the  latter  differing  from  creatin  in  con- 
taining one  molecule  less  of  water.  The  quantity  of  creatinin  in 
the  urine  of  man  a  day  is  about  1.12  grammes. 

Hippuric  acid  is  excreted  in  the  urine  of  man  to  the  extent  of 
about  0.7  gramme  in  twenty-four  hours.  Foods  like  vegetables, 
which  contain  substances  that  yield  benzoic  acid,  increase  the  out- 
put, since  a  union  of  benzoic  acid  and  glycocoll  taking  place  in 
the  kidney  forms  hippuric  acid.  Some,  however,  is  the  result  of 
proteid  putrefaction  in  the  intestines. 

Conjugated  sulphates  are  ethereal  salts  of  organic  compounds  of 
the  aromatic  and  indigo  series.  Among  the  most  important  organic 
radicals  are  phenol,  cresol,  indol,  and  skafol.  These  are  formed 
by  putrefactive  processes  in  the  intestines  from  proteids,  and  are 
partly  excreted  in  the  faeces  and  partly  passed  into  the  blood. 
Since  they  are  injurious  they  are  combined  with  sulphuric  acid  to 
form  the  conjugate  sulphates,  which  are  harmless.  Sulphur  is  also 
excreted  as  simple  sulphates  and  as  unoxidized  sulphur  compounds. 

Water. — The  quantities  lost  through  the  kidneys  and  skin  stand 
in  inverse  proportion  to  one  another.     Since  water  lost  through 


si-ynirnoss  nr  tuk  skix.  47 

the  skill  aHVcts  llic  iioniial  coiistitwliitii  of  the  iiriiic  lliriiiit:li  \\u: 
inv'.li'iiii  of  llu'  l)lo()(l,  it  is  to  l)i'  rxpcctcd  that  otiicr  siii)Slaiiccs  in 
ill,'  riiculatioii  niii^iit  liave  similar  iiilliicncr.  Tiiis,  as  a  iiialtcr 
of  fad.  is  true.  A  tomporarv  alti-ralion  of  llu',  lilood  liy  the 
a')sjori)tit»ii  of  large  (|iiaiitilii's  of  waici- ami  ilu'  jn-esenee  ol"  diurctitw 
iaereases  lln'  ilow  of  water  from  the  kidneys.  It"  saline  diurcticx 
(potassium  nitrate,  soiliiiin  chloride,  urea,  dextro.se,  etc. )  are  iii- 
jectt'd  into  i hr  lilood.  an  al)iindant  secretion  soon  takes  place, 
uiiicli  is  accoiniianiiMl  liv  an  cnlarii-cnicnl  of  ihc  ki<lney  and  a 
slii,dit  rise  of  hlood-pressure.  It  has  been  shown  that  the  power  of 
these  diuretics  is  proportional  to  their  molecular  weights,  and  it  is 
tht'rcfore  highly  proi)al)le  that  through  their  osmotic  power  they 
withdraw  water  from  the  tissues  to  tiie  Mood.  The  diuresis  which 
they  bring  about  lasts  only  as  long  as  the  blood-pressure  remains 
above  normal. 

Other  diuretics  are  caffnn  and  <l!(/if<(lis.  If  •]  grain  of  catfein 
is  injected  into  the  circulation,  the  kidney  at  first  contracts  in  vol- 
ume and  the  secretion  of  water  is  stoi)ped.  Soon,  however,  an 
expansion  takes  place  and  a  C()i)ious  urinary  flow  results.  The 
general  blood-pressure  is  also  lessened  and  then  heightened.  C'af- 
fein  seems  to  act  on  the  renal  vessels,  diminishing  ami  then  aug- 
menting the  flow  of  blood  through  the  glomeruli.  Digitalis  is 
rather  uncertain  in  its  action  as  a  diuretic.  It  slows  and  strength- 
ens the  heat  of  the  heart  in  certain  subjects;  increasing  the  arterial 
pressure  and  lowering  the  venous  pressure,  which  favors  the  flow 
of  blood  through  the  kidney,  and  produces  an  increase  in  the 
amount  of  water  in  the  urine. 

Inorganic  Salts. — Those  of  the  urine  are  chiefly  the  chlori(Jt'-'i, 
pliDsjtlidlrs  and  sit/jilnttfs  of  the  (ilkuVirx  and  (ilkaliiip  rartlis. 
Thev  are  taken  into  the  body  partly  as  such  and  jiartly  in  the 
structure  of  proteids.  Chloride  t)f  sodium  occurs  to  the  greatest 
extent,  amounting  to  about  1")  grannnes  in  a  day's  urine. 

SECRETIONS  OF  THE  SKIN. 

The  perspiration  is  a  colorless  rKpiid  with  a  peculiar  odor,  a 
salty  taste,  an  acid  reaction,  and  a  specific  gravity  of  1004.  The 
amount  formetl  varies  enormously  with  the  temperature,  with  ex- 
ercise, with  psychical  an<l  pathological  conditions,  but  may  be 
put   at   an   average  of  from   TOO  to  !•()()  grammes  a  day,  a  little 


48  SECRETION. 

more  than  half  the  total  of  urine  excreted.  Its  constihienU  are 
water,  inorganic  salts,  traces  of  fat,  fatty  acids,  cholesterin,  and 
urea.  Sodium  chloride  forms  from  2  to  3.5  parts  in  a  thousand, 
The  urea  of  perspiration  in  determinations  of  destroyed  proteid  is 
usually  neglected.  During  extraordinary  muscular  work  the 
nitrogen  eliminated  by  the  skin  amounts  to  0.7  or  0.8  gramme. 
Sweat-glands  are  found  over  the  entire  surface  of  the  skin,  with 
the  exception  of  the  external  ear.  Their  total  number  is  about 
2,000,000. 

Insensible  perspiration  increases  in  quantity  with  increase  of 
temperature  until  a  certain  critical  point  is  reached,  when  it  is 
markedly  increased  and  appears  as  visible  sweat.  The  percentage 
of  carbon  dioxide  is  increased  at  the  same  time.  Normally  the 
glands  are  stimulated  by  exercise  and  high  temperature.  In  the 
latter  case  it  is  produced  through  the  central  nervous  system. 
Instead  of  acting  on  the  glands  directly,  the  heat  affects  cutaneous 
sensory  nerves  and  reflexly  excites  the  glands.  Sweating  can  be 
brought  about  by  stimulation  of  the  afferent  nerves  and  by  dysp- 
noea ;  by  the  latter,  even  if  the  cervical  cord  is  sectioned.  Sweat- 
centres  are,  therefore,  surmised  in  the  cord  as  well  as  in  the 
medulla,  but  they  have  not  been  definitely  demonstrated. 

Sebaceous  Secretion. — This  is  an  oily,  semi-liquid  material, 
which  sets  on  exposure  to  air  and  consists  of  ivater,  salts,  albumin, 
cholesterin,  fats,  and  fatty  acids.  Its  function  is  to  keep  the  hair 
oiled,  and  perhaps  to  prevent  too  great  a  loss  of  water  through 
the  skin,  and  also  too  great  an  absorption.  The  sebaceous  glands 
are  usually  found  in  connection  with  hairs  all  over  the  body,  but 
on  the  prepuce,  glans  penis,  and  lips  they  occur  separately.  The 
secretion  of  the  prepuce  is  known  as  smegma  pneput.ii ;  that  of  the 
external  auditory  canal,  as  cerumen ;  that  of  the  skin  of  the  newly 
born  as  vernix  caseosa.  In  the  formation  of  the  secretion  the 
gland-cells  break  down  bodily  and  are  replaced  by  new  cells 
from  the  layer  nearest  the  basement  membrane. 

MAMMARY  GLANDS. 

The  secretion  of  the  mammary  glands  is  an  alkaline,  bluish- 
white  fluid,  having  a  specific  gravity  of  1030.  It  is  a  typical 
emulsion,  consisting  of  a  fluid  plasma  holding  suspended  fat-glob- 
ules.    When  the  secretion  takes  place  from  a  newly  active  gland 


.U.I.V,)M/M'   GLANDS. 


40 


I  here  are,  l)e>»i(k'.s  ilw  fat-jriohules,  (certain  alljimiiiious  Ijudii-s 
known  as  m/ostrnm  n>ipi()ic/cf<,  \vlii(rli  may  1r'  cells  ol"  tin;  gland  or 
tiKiy,  perhaps,  have  their  origin  in  wandering  connective-tissue 
corpuscles.  The  plasma  of  the  milk  consists  of  water  holding  in 
solution  casein,  lucto-ulhumin,  lacto-glohulin,  lacto.><e,  salts,  traces 
of  urea,  creatin,  and  creatinin.  The  i'at-glohules  consist  chiefly 
of  stearin,  palmilin,  and  olcin,  which  upon  standing  rise  to  the 
surface  as  rrcain.  Their  nund)er  in  1  c.c.  of  milk  has  been  esti- 
mated to  he  from  1  to  .">, 7 *><>,( )()().  They  are  not,  as  was  formerly 
i)elieve<l,  surrounded  by  an  albuminous  envelope.  Through  their 
high  refractive  power  they  are  chiefly  responsible  for  the  color  of 
milk.  The  casein  which  is  held  in  solution  by  calcium  phosphate 
is,  however,  partly  the  cause  of  the  color  of  milk. 

The  rcaciloii  of  mi/k  is  often  amphoteric,  and  may,  especially 
ill  carnivora,  be  acid.  Fresh  milk  is  not  coagulated  by  heat,  but 
upon  standing  it  slowly  becomes  acid  through  the  formation  of 
lactic  acid  by  fermentation,  and  will  then  curdle  if  heated.  The 
sctan  forming  on  cooked  milk  is  a  combination  of  casein  and  cal- 
cium. As  it  is  often  necessary  in  infant  feeding  to  replace  the 
mother's  by  cow's  milk,  it  is  im])ortant  to  consider  some  of  the 
differences  between  various  milks.  The  following  table  is  modi- 
fied from  Konig : 


Milk. 


^?o.^hi^    Water.   Casein, 
gravity 


Woman   ....  I  1.027 

Cow  ^ 1.031 

(  (ildstruni  (if  cow.  .    . 

(Joiit 

Sheep 1.034 

Mure i  1.034 

Ass 1  .    .    . 


87.41 
87.17 
74.07 
85.71 
80.82 
90.78 
89.64 


1I( 


84.04 


1.03 
3.02 
4.04 
3.20 
4.79 
1.24 
0.67 


Albumin 

1 

and 

Fat. 

Lactose. 

globulin. 

1.26 

3.78 

6.21 

0.53 

3.69 

4.88 

13.60 

3.59 

2.67 

1.09 

4.78 

4.46 

1.55 

6.86 

4.91 

0.75 

1.21 

5.67 

1.55 

1.64 

5.99 

4.55 

3.13     1 

Ash. 

0.31 
0.71 
l.o6 

0.76 
U.89 
0.35 
0.51 
1.05 


The  rnnipm^lf.lov  of  human  milk  varies  with  the  constitution, 
with  the  state  of  nutrition,  with  age,  with  the  complexion,  at  dif- 
ferent stages  of  lactation,  from  the  two  breasts,  etc.  It  is  distin- 
guished from  coir'n  milk  mainly  by  the  low  percentage  of  proteid 
and  the  high  percentage  of  sugar.  The  difierence  in  the  proteid 
causes   human    milk    to   form   a  more   llocculent  and   more  easily 

l-l'i.v.-. 


50  SEOBETION. 

digested  precipitate  when  coagulated.  Practically  all  the  phos- 
phorus is  in  organic  combination  as  nucleon  and  caseinogen,  and 
is  not,  as  in  cow's  milk,  found  as  pseudo-nuclein.  The  casein  in 
woman's  milk  is  more  difficult  to  precipitate  by  acids,  salts,  and 
rennet  and  is  also  more  easily  redissolved  by  an  excess  of  acid. 

Human .  milk  contains  the  fatty  acids — oleic,  stearic,  palmitic, 
butyric,  caproic,  capric,  and  myristic,  combined  with  glycerine. 
Cow's  milk  contains  in  addition  caprylic  and  arachic  acids. 
Human  milk  is  poor  in  volatile  acids.  The  chief  base  is  potas- 
sium, while  that  of  other  animals  is  calcium. 

The  cells  of  the  mammary  glands,  which  during  pregnancy  be- 
come active  for  the  first  time,  undergo  histological  changes  of 
such  a  nature  that  each  cell  increases  in  size,  undergoes  a  fatty 
metamorphosis,  the  nuclei  divide,  and  then  a  portion,  at  least,  of 
the  cell,  if  not  the  whole  of  it,  disintegrates.  The  fragments  form 
the  constituents  of  the  milk.  There  are  known  instances  where  the 
secretion  of  milk  has  been  suppressed  by  strong  emotions,  epilep- 
tic attacks,  etc.,  indicating  a  control  of  the  central  nervous  system. 
The  connection  between  the  gland  and  tlie  uterus,  which  stand  in 
close  relation,  is  mainly  through  the  blood. 

That  the  secretion  of  milk  may  be  continuous  is  not  known  with 
certainty,  but  it  is  probable  that  as  it  accumulates  in  the  sacculated 
ducts  of  the  gland  the  tension  finally  inhibits  further  secretion. 
The  emptying  of  the  ducts  is  the  normal  stimulus,  either  directly 
or  reflexly,  for  a  renewed  activity  of  the  gland.  Otherwise  the 
cells  undergo  retrogressive  changes,  but  they  never  become  as  they 
were  before  the  first  pregnancy. 

.It 

THYROID. 

The  secretion  of  the  thyroid  is  a  homogeneous,  glairy  liquid, 
known  as  colloid  substance,  and  is  contained  within  the  closed  vesi- 
cles and  surrounding  lymph-spaces  of  the  gland.  Its  composition 
is  not  well  known.  Of  the  bodies  related  to  the  thyroids,  para- 
and  accessory  thyroids,  the  latter  probably  have  the  same  function. 
Complete  removal  of  the  organs,  or  thyroidectomy,  as  it  is  called,  is 
followed  by  a  train  of  symptoms  that  ends  in  death  and  is  more 
fatal  in  the  young  than  in  the  old.  In  dogs  muscular  tremors  and 
spasms  are  accompanied  by  emaciation  and  apathy.  Section  of 
the  motor  nerves  prevents  the  spasms,  indicating  that  they  are  of 


PANCREAS.  51 

conlral  ori<;in.  In  monkeys  tliyroidcctoiny  rcseinMos  uiii.ni(lniin 
in  man.  The  sym|)toms  an;  Jina'mia,  failure  of  muscular  and 
menial  power,  dryness  of  the  skin,  loss  of  hairs,  ancl  swelling  of 
tlu-  sidiciitaneons  1  issue.  They  may  he  prevented  i)y  graflinf^  a 
pii'ce  of  the  tiiyroid  under  tlu;  skin  or  anywhere  in  the  ahdoniinal 
cavity.  In  human  hein^^s  favorahle  results  have  heen  obtained 
l>v  the  inijestion  of  thvroid  extracts  and  hv  feedin;j^  with  the  fresh 
-land. 

It  appi'ars  that  th"  ihyroitis  and  accessory  thyroids,  on  the  one 
hand,  dilier  from  llu'  parathyroids,  on  the  oilier,  in  that  removal 
of  the  lirsl  causes  slow  trophic  disturbances,  while  removal  of  the 
last  results  in  acute  disturbances  and  quick  death.  These  glands 
may  be  regarded  as  functioning  in  two  ways.  They  may  either 
antagonize  toxic  substant-es  that  are  found  in  the  blood,  or  may 
produce  a  secretion  which  is  necessary  to  the  metabolisjn  of  the 
i)oily  in  general,  and  particularly  of  the  central  nervous  system. 
There  hius  been  isolated  from  the  thyroid  a  substance  which  is 
peculiar  iu  containing  a  large  percentage  of  iodine,  and  which  is 
tor  the  most  part,  while  in  the  gland,  combined  with  proteids.  It 
has  been  named  iodothyrhi.  The  parathyroids  contain  relatively 
larger  amounts  of  this  substance.  It  is  quite  stable,  and  possesses 
llie  same  beneficial  action  as  the  thvroid  extract. 


PANCREAS. 

Extirpation  oi'  the  pancreas  is  followed  by  the  apj)earance  of 
sugar  in  the  urine,  polyuria,  emaciation,  muscular  weaknes.s,  and 
ultimate  death.  The  result  depends  upon  the  completeness  of  the 
removal  ;  one-fourth  to  one-fifth  of  the  gland  remaining  prevents 
the  svniptoms.  As  in  the  case  of  the  thyroid,  they  may  be  pre- 
vented bv  grafting  a  portion  of  the  gland  anywhere  under  the 
skin  or  in  the  abdominal  cavity.  The  sugar  of  the  blood  is  in- 
crea.sed  I'rom  0. 15  to  O.-jO  jier  cent.,  and  the  glycogen  of  the  liver 
disappears.  C'arbohvdrate  foods  are  not  used  \\\\  but  are  a)i]>a- 
rently  eliminated  in  the  urine.  It  is  believed  that  the  ])ancreas 
gives  oft'  a  substance  that  is  necessary  either  to  the  consumption 
of  sugar  in  the  body  or  else  hinders  the  liberation  of  sugar  from 
sugar-producing  organs.     It  may  be  of  the  nature  of  an  enzyme. 


52  SECRETION. 


LIVER. 


The  liver  in  its,  production  of  urea  and  glycogen  resembles 
those  organs  producing  interual  secretions.  The  blood  of  the 
portal  vein  brings  sugars  and  proteids  to  the  liver,  which  are  con- 
verted into  animal  starch  or  glycogen  (CgHjgOg)u.  The  latter  can 
be  seen  in  the  liver-cells  microscopically.  As  the  demand  arises, 
it  is  by  a  process  of  hydration  changed  to  dextrose,  and  secreted 
back  into  the  blood,  to  be  made  use  of  by  other  tissues.  Urea  is 
made  by  the  liver-cells  from  ammonia  compounds,  and  secreted 
into  the  blood,  to  be  excreted  by  the  kidney.  In  both  cases  the 
liver  functions  for  the  good  of  the  entire  body.  It  is  possible  that 
it  may  also  be  essential  to  the  conservation  of  iron  of  broken-down 
hsemoglobin  and  in  the  formation  of  conjugate  sulphates. 

SUPRARENAL    CAPSULES   (ADRENAL   BODIES). 

The  removal  of  these  bodies  is  more  quickly  fatal  than  the 
removal  of  the  thyroids,  death  occurring  in  a  few  hours  or  a  few 
days.  The  symptoms  are  muscular  weakness,  loss  of  vascular 
tone,  and  great  prostration,  resembling  those  of  Addison's  disease, 
which  involves  lesions  of  the  adrenals.  The  glands  may  normally 
be  supposed  to  remove  toxic  substances  from  the  body,  which  are 
formed  chiefly  in  the  muscles.  Aqueous  extracts  of  the  medulla 
of  the  gland  injected  into  the  vessels  of  an  animal  will  cause  a 
marked  slowing  of  the  heart-beat  and  a  simultaneous  rise  of  blood- 
pressure  if  the  vagi  are  intact.  When  the  latter  are  cut,  the 
heart-beat  is  increased  in  its  rate  and  the  blood-pressure  rises 
enormously.  The  effect  is  due  to  a  direct  action  upon  the  muscles 
of  the  blood-vessels.  It  requires  very  little  of  the  substance  to 
produce  maximum  effects,  but  they  are  of  a  transitory  nature.  It 
has  been  found  to  be  present  in  the  adrenal  vein,  and  is  increased 
by  stimulation  of  the  splanchnic  giving  evidence  of  distinct  secre- 
tory fibres  to  the  gland-cells.  An  imstable,  basic  body,  called 
epinephrin,  has  been  isolated,  which  gives  the  same  physiological 
effects  when  injected  into  the  circulation  as  does  the  extract. 

PITUITARY  BODY. 

Extracts  of  the  infundibular  portion  of  the  pituitary  body 
cause  a  rise  of  blood-pressure  and  a  slowing  of  the  heart-beat 


TESTIS  AXD    OVARY     rUVMI'S   <:L.\SI>   AM>  SI'LIIES.      53 

wln'ii  injcctiMl  iiitravciiou.sly.  Kciiioval  i.A'  tlu-  pituitary  body  is 
followiMl  liy  muscular  tri'inor.s  spasms,  ilys|)im.'a,  au«l  Wt-atii.  I'allio- 
loiricallv,  legions  of  \\\v  pituitary  ar<;  coniiectcil  with  a  (litsejuje  of 
the  bones  causing  hypertrophy,  known  a.s  acromnjali/. 

TESTIS  AND  OVARY. 

Hrown-S.'(piaril  lirst  invusliirated  tin-  internal  secretion  of  the 
testis.  He  showed  that  an  extract  of  the  <;land  or  of  the  spermatic 
fluid  when  inji-cted  un<ler  the  skin  will  produce  mental  and  phy- 
sical vi^for  in  cases  of  prostration,  neurasthenia,  and  old  a<;e.  The 
active  sul)stance  has  l)een  isolatetl  and  called  .7>ermt/(  (C"JI,,N,). 
It  is  not  essential  to  life,  since  the  testes  may  he  removed  without 
fatal  results.  It  is  a  well-known  fact  that  ovariotomy  and  prema- 
ture menopause  may  he  followed  by  abnormal  mental  symptoms 
and  often  by  a  irain  in  weiirht.  In  oKfeoinalaciti,  a  disease  giving 
rise  to  a  .softening  of  the  bones,  removal  of  the  ovaries  has  been 
found  to  e.xert  a  favorable  influence.  In  dogs  complete  ovariotomy 
is  i"ol lowed  by  a  lessening  of  the  consumption  of  oxygen,  which  is 
increased  again  by  feeding  with  ovarian  extracts.  These  facts 
show  the  influence  of  the  ovaries  upon  the  general  nutrition. 

KIDNEY. 

tSome  investigators  have  describeil  the  effects  of  extract?  of  the 
kidney  which  cause  a  rise  of  blood-pressure.  The  active  substance 
has  been  named  rennia. 


THYMUS  GLAND  AND  SPLEEN 

Extracts  of  the  thymus  and  spleen  seem  to  have  no  specific 
effect. 

The  function  of  the  latter  organ  is  very  little  understoiMl. 
It  may  be  renjoved  from  the  organism  without  serious  injury, 
giving  rise,  it  is  a.s.serte(l,  to  an  enlargement  of  lymph-glands  and 
to  an  increa.se  in  the  amount  of  bone-marrow.  It  has  also  been 
found  that  the  lunnber  of  red  blood-corpuscles  is  diminisheil.  The 
following  suggestions  of  the  function  of  the  S|)leen  have  been 
offered  : 

1.  That    the   spleen    manufactures    blood-corpuscles.      This    is 


54  SECRETION. 

without  doubt  true  iu  man  duriug  foetal  life  and  at  birth,  but  it  is 
not  known  that  it  contiuues  throughout  life. 

2.  That  the  spleen  destroys  the  red  blood-corpuscles.  The  evi- 
dence for  this  theory  is  that  spleen  tissue  is  rich  in  iron-holding 
compounds,  and  that  certain  amoeboid  cells  of  the  spleen  have 
been  seen  apparently  ingesting  and  destroying  red  blood-cells. 

3.  That  the  spleen  produces  uric  acid.  Uric  acid  is  found  in 
the  spleen,  but  also  in  all  lymphoid  tissue. 

4.  That  the  spleen  produces  an  enzyme  which  is  carried  to  the 
pancreas  iu  the  blood,  converting  trypsinogen  into  trypsin.  A 
striking  feature  of  the  spleen  is  its  rhythmic  movements.  It  under- 
goes a  slow  expansion  and  relaxation,  with  definite  periods  of 
digestion.  These  are  due  to  vasomotor  changes,  the  maximum 
vasodilatation  occurring  about  the  fifth  hour  after  a  meal.  In  cats 
and  dogs  there  are,  in  addition,  rhythmical  changes  taking  place 
from  minute  to  minute  which  serve  to  maintain  a  constant  circu- 
lation through  the  organ.  The  spleen  is  well  supplied  with 
nerves,  stimulation  of  which  produce  a  contraction. 

The  chemical  substances  found  in  the  spleen  are  interesting, 
since  they  indicate  a  marked  metabolism.  There  is  a  large  per- 
centage of  iron  in  an  unknown  organic  combination.  In  addition, 
there  are  fatty  acids,  fats,  cholesterin,  xanthin,  hypoxanthin, 
adenin,  guanin,  and  uric  acid. 

QUESTIONS  ON   CHAPTER  II. 

What  is  meant  by  the  term  secretion  ? 

Distinguish  between  external  and  internal  secretions  and  excretions. 

Give  proofs  that  gland-cells  are  active  during  secretion. 

Define  filtration,  diffusion,  and  osmosis. 

What  is  the  source  of  saliva? 

Discuss  albuminous  and  mucous  glands  and  their  products. 

Describe  the  histological  changes  in  salivary  glands  during  activity. 

What  are  zymogen  granules  ? 

Describe  the  nerve-supply  of  the  salivary  glands. 

Give  results  of  the  stimulation  of  chorda  tympani  and  sympathetic  nerves. 

What  are  the  proofs  that  secretion  is  not  simply  due  to  increased  blood- 
supply? 

What  is  the  relation  of  the  composition  of  saliva  to  the  strength  of  stimu- 
lation ? 

Give  Heidenhain's  and  Langley's  views  on  secretion. 

What  is  paralytic  secretion  ?     Antilytic  secretion  ? 

Explain  changes  in  secretion  produced  by  drugs. 

Give  mechanism  of  normal  secretion  of  saliva. 

Discuss  the  cells  of  the  gastric  glands. 

Give  the  results  of  stimulation  of  their  nerve-supply. 


QUESTIONS  0.\  CUM'TI-Jl   //.  55 

III  wlial  ways  umy  tlicRastric  juici^  he  caused  to  (low? 

Dcsi  tIIk!  cliaiifjos  in  ci-lls  <liiriii;;  activity. 

Describe  the  cells  of  the  pancreas  and  the  change.*)  they  uudcrgo  when 
active. 

What  is  the  effect  of  stimulation  of  the  medulla  on  (lancreutic  secretion? 

Discuss  resiilt.s  of  stimulation  of  nerve-siii>ply  to  pancreas. 

What  causes  the  pancreatic  juice  to  flow  normally? 

How  luucli  liile  is  secreted  in  a  day? 

What  is  the  relation  of  hile-.socretion  to  the  hlood-supi)ly ? 

Descrihe  the  cH'ect  on  l)ile-secretion  produced  hy  stimulation  of  the  cord 
and  s])laiichiiic  nerves. 

Wliat  can  lie  said  of  the  influence  of  the  nerve-sui)ply  on  the  cells  of  the 
intestinal  mucous  memhraiie? 

Discu.ss  serous  secretions. 

What  is  the  nerve-supply  of  the  lachrymal  glands? 

What  are  tears? 

Are  there  secretory  tilires  to  the  kidney? 

(live  the  relation  of  the  blood-sujjply  to  the  secretion  of  urine. 

What  is  an  oncometer? 

Descrihe  the  nerve-sui)ply  to  the  kidney. 

In  what  way  is  the  secretion  of  urine  influenced  hy  nerves? 

(live  evidence  that  cells  are  active  in  the  formation  of  urine. 

Where  iu  the  kidney  does  the  excretion  of  water  and  s;ilts  take  place? 

Hive  reasons  for  thinking  that  the  cells  of  the  glomerular  epithelium  are 
active  in  secretion. 

How  is  the  action  of  diuretics  explained? 

Descrihe  the  urine  and  state  the  amount  formed. 

What  is  the  color  of  the  urine  due  to? 

Why  is  the  urine  of  complex  comjiosition  ? 

What  are  the  most  important  constituents  of  urine? 

Discuss  the  urea  of  the  urine. 

What  are  the  i)roofs  that  the  kidney  does  not  manufacture  the  urea? 

What  evidence  is  there  that  urea  is  formed  in  the  liver? 

What  is  the  precursor  of  the  urea  iu  the  blood? 

Discuss  the  uric  acid  of  the  urine. 

What  is  the  source  of  the  xanthin  bases? 

What  is  the  source  of  creatinin  ? 

Discuss  hippuric  acid  of  the  urine. 

Wh;it  are  conjugate  suli)hates? 

In  what  other  forms  is  sulphur  excreted  from  the  body? 

What  is  the  relation  of  the  water  lost  through  the  kidney  and  the  skin  ? 

Discuss  the  action  of  caffein  and  digitalis  on  the  secretion  of  water  by  the 
kidney. 

What  are  the  inorganic  salts  of  the  urine? 

Discuss  the  secretions  of  the  skin. 

How  are  the  swi'at-glands  stimulated  to  activity? 

Wliat  is  the  method  of  action  of  temperature  in  jiroducing  secretion  of 
sweat  ? 

Descrihe  the  properties  and  method  of  fonnation  of  the  sebaceous  secretinu. 

Describe  the  secretion  of  the  mammary  glands. 

What  are  colostrum  corpu.scles?  C'omjjare  human  milk  with  that  of  the 
cow. 

Describe  the  liistologi<al  changes  that  take  jilace  in  the  formation  of  milk? 

What  facts  indicate  a  control  of  the  central  nervous  system  over  the 
activity  of  the  mammary  glands? 


50  DIGESTION. 

Describe  the  normal  secretion  of  milk. 

What  is  colloid  substance  ? 

(Hve  the  symptoms  of  thyroidectomy  in  man  and  in  the  lower  animals. 

How  can  the  spasms  following  thyroidectomy  be  shown  to  be  of  central 
origin  ? 

How  may  the  symptoms  of  thyroidectomy  be  prevented? 

In  what  way  do  the  parathyroids  differ  from  the  thyroids? 

What  is  the  function  of  the  thyroid  gland  ? 

What  is  iodothyrin  ? 

Describe  the  symptoms  of  extirpation  of  the  pancreas. 

How  may  the  symptoms  be  prevented  ? 

What  is  the  function  of  the  internal  secretion  of  the  pancreas  ? 

Describe  the  glycogenic  function  of  the  liver. 

What  are  some  of  the  functions  of  the  liver? 

What  are  the  symptoms  of  removal  of  the  suprarenal  capsules? 

The  symptoms  of  what  disease  in  man  do  they  resemble  ? 

What  is  the  function  of  the  suprarenal  capsules? 

Describe  the  effects  of  injections  of  extracts  of  the  medulla  of  the  gland. 

Explain  the  cause  of  the  results  obtained. 

What  evidence  of  secretory  fibres  to  the  suprarenal  capsules? 

Describe  the  physiological  effects  of  epinephrin. 

Give  the  effects  of  injections  of  the  pituitary  body. 

What  disease  is  connected  with  lesions  of  the  pituitary? 

Give  the  source  and  physiological  action  of  spermin. 

What  evidence  that  the  ovaries  may  have  an  effect  on  the  general  nutri- 
tion ? 

Give  the  source  and  physiological  action  of  rennin. 


CHAPTER    III 
DIGESTION. 


Substances  that  constitute  food  may  occur  in  a  gaseous,  fluid, 
or  solid  state.  When  in  the  last  condition  it  is  merely  in  a  limited 
number  of  cases  that  it  may  be  ingested.  For  most  organisms 
the  solid  must  be  converted  into  the  liquid  form.  This  trans- 
formation is  termed  digestion  and  is  effected  by  ferments.  What 
we  call  food  appears  to  consist  of  the  most  varied  substances,  but 
upon  analysis  is  found  to  be  composed  of  a  small  number  of  food- 
stuffs.    There  are  seven  classes. 

1.  Proteids  are  absolutely  essential  to  animal  organisms,  since 
they  are  the  sole  available  source  of  nitrogen.  They  serve  for 
the  repair  of  old  tissue,  for  the  formation  of  uQyv  tissue,  and  as  a 
source  of  energy.  They  contain  the  elements  C,  H,  N,  O,  S,  and 
sometimes  P  and  Fe.  Hundreds  of  atoms  are  contained  in  a 
molecule ;  the  formula  for  egg-albumen,  for  instance,   has   been 


.1  /./; I 'MiXdins   c. I nnoii ydiiates.  57 

^rivcn  as  ^'.,,„II,..,^fi..^^,fi'^>-  ^^wiiit;  to  tlu;  uncertainty  <><'  their  slrue- 
liire.  classiticalioiis  of  proteiils  vary  in  minor  ways.  Il  will  l)e 
sniliciiiil  lo  hear  in  mind  thai  there  are  utinji/c  and  eoiiihincd  jtro- 
t'iils.  As  concrete  (examples  of  the  first  may  he  ^iven  ej^g- 
alhunirii  and  lihrin  ;  of  the  second,  iuemoglohin,  mucin,  and 
casi'in.  SiinpU'  j>rotei<ls  may  he  divide<l  into  a/hnmint,  ijlobnliax, 
(i/l)ii)iio.-<r.-<.  pi'jitoiii's,  iilhitminalc.^  and  roaiiiilalcd  jiroteuln.  iSatura- 
tion  of  the  solution  with  magnesium  sulphate  throws  down  tiie 
glohulin,  i)Ut  not  alhumin.  Saturation  with  anunonium  sulphate 
throws  down  ali)nmin.  glohulin,  and  alhumosi-,  hut  not  peptone. 
The  presence  of  proleid  in  solution  may  he  detected  hy  the  follow- 
ing test*; : 

(a)  Biuret  YV.s/. — To  the  solution  lo  he  tested  add  an  ecjual 
volume  of  strong  sodium  hydrate.  HeJit  to  hoiling-point,  and  adil 
one  or  two  drops  of  dilute  cojiper  sulphate  solution.  Reaction  : 
a  /)i)ih  color,  which  is  due  lo  the  diamide  group  in  the  proteid 
molecule. 

( /))  Milfoil's  Text. — To  the  solution  to  he  tested  add  two  or  three 
drops  of  Millon's  reagent.  This  reagent  is  made  by  dissolving  in 
the  cold  one  })art  of  mercury  in  an  e(iual  part  by  weight  of  con- 
centrated nitric  acid.  To  effect  an  entire  solution  a  gentle  heat 
must  be  finally  applied,  and  then  two  volumes  of  water  are  added. 
If  proteid  is  present  in  the  solution,  a  white  precipitate  forms 
which,  on  boiling  for  several  minutes,  turns  red.  This  reaction  is 
due  to  an  aromatic  nucleus,  since  it  is  given  by  phenol  and  tyrosin. 

(<•)  Heller  K  Ted. — To  the  solution  to  be  tested  add  an  equal 
volume  of  concentrated  nitric  aciil  carefully,  so  as  not  to  mix. 
The  jiroteid  is  precipitated. 

((/)  To  about  5  c.c.  of  the  solution  to  be  tested  add  two  drops 
of  strong  acetic  acid  and  then  one  or  two  drops  oi  jxAa-^sium  ferro- 
rjiatiidr.     T'roteid  precipitates.     This  is  a  very  delicate  test. 

2.  Albuminoids  resemble  and  are  derived  from  true  proteid, 
but  cannot  take  the  place  of  the  latter  as  a  source  of  nitrogen  to 
animals.  They  are  of  com])lex  structure,  and  have  the  same  nu- 
tritive value  as  <arboliydrates.    (Jelatin  is  a  well-known  example. 

•  !.  Carbohydrates  include  starclu's,  sugars,  gums,  etc.  They 
are  divisible  into  three  main  grouj)S — vKDio.mecharides,  dimc- 
cliaride.%  and  poli/saccliaridex.  Those  of  the  first  group  may 
possess  either  the  structure  of  an  aldehyde  alcohol,  when  they  are 
known  as  ald<)-<es.  or  of  a  ketone  alcohol,  when  thev  are  known  a? 


58  DIGESTION. 

ketoses.  Dextrose  is  an  example  of  an  aldose,  while  levulose  is 
an  example  of  a  ketose.  The  most  familiar  example  of  a  mono- 
saccharide is  dextrose  (C^H^fi^).  It  may  be  detected  by  boiling 
with  Fehling's  solution.  Disaccharides  are  represented  by  ea??e- 
sugar  (C^^H^fi^J.  Not  reducing  Fehling's  solution,  it  may  be 
detected  by  the  fermentation  test.  This  test  may  be  made  as  fol- 
lows :  The  solution  to  be  tested  is  rubbed  up  with  a  little  yeast 
and  placed  in  a  U-shaped  tube,  one  arm  of  which  is  closed.  The 
closed  arm  must  be  filled  completely  and  free  from  air.  After 
twenty-four  hours'  exposure  to  a  warm  temperature  an  accumula- 
tion of  gas  in  the  closed  end,  due  to  fermentation,  denotes  the 
presence  of  sugar.  Polysaccharides  are  represented  by  starch 
(CgHjgOjju-  The  value  of  the  („)  has  been  placed  at  from  6  to 
200.  This  substance  is  insoluble  in  water,  except  at  a  high  tem- 
perature, which  produces  solul^le  starch  and  perhaps  many  minor 
hydrolytic  products.  It  may  be  detected  by  the  addition  of  iodine 
solution,  a  blue  color  resulting. 

4.  Fats,  like  carbohydrates,  consisting  of  carbon,  hydrogen, 
and  oxygen,  are  more  valuable  sources  of  energy,  but  not  so 
cheap  or  so  easily  digested.  Chemically,  fats  are  esters  resulting 
from  the  union  of  glycerine  with  a  monobasic  fatty  acid.  Ordinary 
fats  are  mixtures  of  the  three  chemical  fats — stearin,  pabnitin,  and 
oleiii.  They  are  readily  split  by  hydration  into  their  components, 
glycerine  and  fatty  acid.  The  latter  uniting  with  a  base  gives 
rise  to  saponification — e.  g.  : 

stearin.         4-  Potassium  hydrate  =  Potassium  stearate     +  Glj'ceriue. 

(C,jH„0).  J  o^   ^  3  H  I  o  ^  3  (C„H„0  J  ^^  ^  ^H.  |  ^^ 

5,  6.  Water  and  salts  are  absolutely  essential  to  life,  since  the 
tissues  must  maintain  a  certain  composition  in  water  and  salts 
which  are  continually  being  lost,  so  that  they  must  be  replaced  in 
the  food. 

7.  Oxygen  being  absolutely  essential  to  the  continued  existence 
of  life,  may  in  this  sense  be  considered  a  food.  Condiments  and 
flavors  have  a  beneficial  effect  in  promoting  the  flow  of  digestive 
juices  and  in  increasing  the  palatableness  of  the  food.  Mustard 
and  pepper  increase  absorption  from  the  stomach. 

These  classes  of  food-stuffs  enter  in  varying  proportions  into  ^U 


suhsfaiKTS  Ihnt  cniistitiiU'  tlif  looil  of  aiiimiils,  an<l  <lurinf^  dijrcs- 
tioii  are  cliaiiircd  clirmirally  l»y  iK'iii;,^  l)rou<,'lit  into  contact  willi 
tlie  (lij^e-slive  juices.  Tlit;  active  tiiihstaiices  iu  the  latter  are  coiii- 
|)lex  ori,fanic  hoilies  tenned  enzumrti.  They  are  non-living'  suW- 
stanees  eontainiug  nitrogen,  anil  are  soluhle  in  water  ami  glycer- 
ine; destroyed  hy  temperatures  from  (J0°  to  80°  C,  and  inhibited 
l)v  cold  and  hy  the  proilucts  of  their  own  activity.  The  (■(kk/u- 
htt'nni  frrmeiifx  are  an  exception  to  tlie  statement  that  ferments  are 
inhihited  hy  tlie  products  of  their  activity.  Tlie  most  peculiar 
propi'rtv  of  all  ferments  is  that  in  their  action  they  are  not  u-sed 
up,  .-^o  that  a  small  amount  of  ferment  will  change  an  almost  in- 
definite amount  of  the  substance  acted  upon.  They  have  been 
.Slid  to  act  by  caial)i.'<tx,  which  means  by  their  mere  presence.  It 
is  conceivable  that  a  ferment  may  act  through  its  physical  proper- 
ties or  through  certain  chemical  changes  that  it  undergoes,  but 
which  leave  it  ultimately  iis  it  was  at  tlie  beginning.  Both  possi- 
bilities may  be  illustrate<l  by  phenomena  from  inorganic  nature. 
For  instance,  a  trace  of  iodine  added  to  amorphous  phosphorus 
will  convert  the  entire  ma.<s  into  red  phosphorus.  Tlie  iodine  un- 
dergoes no  chemical  change,  but  acts  through  its  physical  proper- 
ties, p()s.sibly  by  inducing  a  more  active  molecular  vibration  iu 
the  phosphorus,  so  that  it  assumes  a  more  staple  structure. 

Chittenden  hsis  given  an  example  illustrating  the  other  pos.sible 
method  of  action  of  enzymes.  Carlion  monoxide  and  oxygen,  when 
perfectly  drv,  cannot  be  made  to  unite  by  means  of  an  electric 
spark,  l)Ut  if  a  small  (piantity  of  water  vapor  is  pre.><ent.  they  com- 
bine readily.  The  following  eijuations  explain  the  reactions.  In 
them  it  is  .seen  that  water  takes  part  in  the  reaction,  but  remains 
finally  as  it  was  at  the  beginning  : 

2H./)  +  CO  +  O,  =  C0(  OH )..  +  H,0,. 
H.,0., +  CO==CO(OH):, 
2C0(0H).,  =  2C0,  +  2H,p. 

There  is  much  more  certainty  in  regard  to  the  changes  proiluce<l 
in  the  bodies  u])i)n  which  the  enzymes  have  acted.  The.se  are  in 
all  cases,  probalilv,  hi/dnillon  chaHi/rx — /.  r.,  the  substances  acted 
upon  take  u|)  water  and  then  break  down  into  simpler  combina- 
tions.      The  reasons  for  this  belief  are  as  follows: 

1,    Enzymes  act  only  in  the  presence  of  water. 


60  DIGESTION. 

2.  In  many  cases  an  examination  of  the  substances  before  and 
after  fermentation  show  directly  a  taking-up  of  water. 

3.  The  action  of  ferments  may  be  imitated  by  dilute  acids  or 
alkalies,  which  are  the  most  powerful  hydrolytic  agents  known. 

Enzymes  are  classified  according  to  the  results  that  they  bring 
about.  They  may  be  proteolytic,  amylolytic,  fat-  and  sugar-split- 
ting, and  coagulating  ferments. 

SALIVARY  SECRETION. 

The  saliva  is  a  transparent,  viscid  fluid  of  a  specific  gravity  of 
1002  to  1008.  It  is  normally  alkaline  in  reaction.  The  amount 
formed  in  twenty-four  hours  is  about  1500  c.c.  When  taken  from 
the  mouth,  it  is  known  as  mixed  saliva,  and  is  turbid,  owing  to 
suspended  particles  of  matter.  It  contains  characteristic  salivary 
corpuscles,  which  are  probably  altered  leucocytes.  Chemically  it 
consists  of  99.5  per  cent,  water,  holding  in  solution  salts,  proteids, 
and  the  ferment  jjtyalin.  The  viscidity  is  due  to  a  glycoproteid, 
mucin.  Saliva  keeps  the  mouth  moist  in  chewing  and  in  speaking, 
dissolves  certain  substances,  aud  so  brings  them  in  contact  with  the 
organs  of  taste,  makes  swallowing  possible  by  wetting  the  food, 
and  acts  by  means  of  its  ferment  on  starches.  Ptyalin,  by  a  pro- 
cess of  hydratio7i,  converts  starch  to  maltose  through  7iumerous  inter- 
mediate steps.  The  first  change  is  probably  the  formation  of 
soluble  starch  or  amylodextrine,  which,  by  further  action  of  the 
enzyme,  gives  off"  a  molecule  of  maltose,  leaving  a  body  known  as 
erythrodextrin.  The  latter  may  be  detected  by  the  red  color  it 
gives  upon  the  addition  of  iodine.  Erythrodextrin,  by  a  further 
splitting-Off"  of  a  maltose  molecule,  is  converted  into  a  series  of 
achroddextrins,  which  give  no  color  reaction  with  iodine.  These 
are,  by  the  continued  splitting-off"  of  maltose  molecules,  finally  all 
converted  into  maltose.  Ptyalin  acts  in  a  neutral  or  slightly  alka- 
line medium.  Free  hydrochloric  acid  to  the  extent  of  0.003  per 
cent,  stops  its  action,  which,  taken  in  connection  with  the  fact  that 
the  food  remains  in  the  mouth  but  a  very  short  time,  indicates  that 
the  ptyalin  digestion  is  not  very  important  and  is  limited  to  the 
initial  stages,  that  is,  within  the  mouth  only,  as  the  acid  of  the 
stomach  stops  it.  Cooked  starch  is  more  readily  acted  upon  than 
raw,  owing  to  the  fact  that  the  cooking  destroys  the  cellulose 
envelope  that  surrounds  the  starch-grains. 


GASTRIC  JUICE.  01 


GASTRIC  JUICE. 


The  pistric  juice,  wliidi  is  the  next  di^restive  juice  to  act  upon 
foods,  is  a  thin,  nearly  colork-ss  li(|ui(l,  of  slronjr  sicid  reaction  and 
|)cculiar  odor.  Its  s])ecilic  ;^M-avity  varies  from  1001  to  lOlO.  Its 
constitui'iits  are  walcr-hohlin^  peptone,  mucin,  inorganic  sahs, 
iiydrochloric  acid,  and  tlie  v\v/.\\\\v6  jxjixin  and  remiiii.  The  acid 
ot  tlie  gastric  juice  is  proved  to  he  free  hydrochloric  acid  in  tlie 
following  ways : 

(a)  When  all  the  chlorides  are  precipitated  by  silver  nitrate  and 
the  total  chlorine  is  determined,  more  is  found  than  can  he  held 
hy  the  hase*;  present. 

(It)  The  secretion  gives  the  color-tests  for  free  mineral  acids — 
methyl-violet  solutions  are  turned  blue,  etc.  The  amount  of  free 
acid  varies,  hut  may  he  put  at  0.2  to  0.3  per  cent.  It  has  been 
attempted  to  determine  the  source  of  the  hydrochloric  acid  by  in- 
jecting into  the  circulation  of  an  animal  substances  like  ferric 
lactate,  followed  by  potassium  ferrocyanide,  which  react  only  in 
the  presence  of  a  free  mineral  acid  with  the  production  of  Prussian- 
blue.  But  this  only  in  a  general  way  proved  its  formation  in  the 
gastric  mucous  membrane,  leaving  the  method  of  its  formation 
unrevealed.  During  the  active  secretion  of  the  gastric  juice  the 
alkalinitv  of  the  blood  is  increased  and  the  acidity  of  the  urine  is 
decrea.sed,  corroborating  the  view  that  neutral  chlorides  are  decom- 
posed ;  the  chlorine  going  to  form  the  hydrochloric  acid,  while  the 
bases  pa.'is  back  into  the  blood. 

Pepsin  is  a  proteolytic  enzyme  that  acts  only  in  acid  media.  A 
piece  of  fibrin,  for  examj)le.  when  subjected  to  an  artificial  gastric 
juice,  swells  up  and  finally  ])asses  into  solution.  It  is  changed 
into  a  more  dilfusible  firm  of  proteid  called  ])eptone,  but  this 
conversion  takes  place  through  a  number  of  intermediate  steps. 
There  is,  first,  the  formation  of  an  acid-albumin,  which  has  been 
named  ><iiiitonl)i.  Upon  neutralization  of  the  medium,  syntonin  is 
])recipitated,  and  upon  further  addition  of  the  alkali  is  converted 
into  fi/kdli-albinnln,  which  again  passes  into  solution.  Byntonin  is, 
bv  hydrolysis,  changed  to  a  series  of  bodies  known  as  jirimary 
jiroii'oxex.  These  in  turn  undergo  cleavage  with  the  fi)rmation  of 
Hfcouihtni  profi'osfx  or  (Iriifn-ojirdfco-'O'x.  The  latter  finally  become, 
bv  the  further  action  of  the  ferment,  prptoncii. 

Rennin. —  Hesides  pepsin,  the  gastric  juice  contains  an  enzyme 


62  MOESTtON. 

named  rennin,  that  coagulates  milk.  The  latter,  if  left  undis- 
turbed at  the  proper  temperature,  sets  iuto  a  solid  clot  which 
shrinks  and  presses  out  a  clear  yellowish  liquid  called  lohey.  The 
curd  of  human  milk  is  not  a  solid,  but  is  deposited  in  loose  floc- 
culi.  Rennin  acts  upon  the  caseinogen,  causing  hydrolytic  changes, 
with  the  formation  of  ])aracasein  and  whey  proteid.  The  first 
unites  with  calcium  salts  and  is  precipitated  as  the  curd.  The 
conversion  of  starch  by  ptyalin  may  continue  within  the  stomach 
for  some  time  in  the  interior  of  the  food  boli  which  were  formed 
in  the  mouth.  It  has  been  shown  that  cane-sugar  may  be  con- 
verted to  dextrose  and  levulose  in  the  stomach,  but  otherwise  car- 
bohydrates are  not  acted  upon.  Fats  are  liquefied  by  the  heat  of 
the  stomach,  and  mechanically  mixed  with  other  food-substances. 
Albuminoids  undergo  changes  analogous  to  those  of  proteids. 
The  mixture  of  food-substances  passing  from  the  stomach  to  the 
small  intestine  is  known  as  chyme. 

PANCREATIC  JUICE. 

In  the  intestine  the  food  undergoes  the  greatest  digestive  changes. 
The  pancreatic  j  uice  which  enters  the  upper  portion  of  the  intes- 
tine is  a  clear,  colorless,  alkaline  liquid,  of  a  specific  gravity  of 
about  1015.  Its  composition  varies,  consisting  of  water,  salts,  and 
organic  bodies.  It  contains  the  three  important  enzymes — trypsin, 
amylopsin,  and  steapsin.  Trypsin  acts  on  proteids  in  alkaline 
media,  but  may  also  act  in  neutral  and  weak  acid  media.  The 
changes  effected  are  similar  to  those  which  result  from  the  action 
of  pepsin,  but  the  action  is  more  rapid,  the  primary  proteoses 
being  omitted.  The  proteid,  instead  of  swelling  as  in  peptic  diges- 
tion, undergoes  erosion  and  disappears.  It  has  been  found  that 
tryptic  digestion  will  go  further  than  peptic  digestion,  inasmuch, 
that  of  the  peptone  formed,  a  portion  undergoes  further  changes 
into  amido-acids  and  nitrogenous  bases,  and  is  designated  as  hemi- 
peptone.  The  portion  that  resists  further  change  is  called  anti- 
peptone.  Together  they  are  known  as  amphojyeptones.  The  most 
important  of  the  simpler  organic  bodies  formed  are  leucin  and  ty- 
rosin.  They  are  of  smaller  molecular  weight  and  of  simpler 
structure  than  peptones,  and  since  they  have  little  available  energy 
and  are  useless  in  the  repair  of  proteid  tissue,  their  significance  is 
problematical. 


Ami/lo/mn  is  the  ferment  of  the  piincreatic  juice  that  avia  on 
starches,  and  is  idnillm/  wHli  plyulin.  It  forms  an  end  product 
— maltose — and  iiilciiiicdiate  dexlrins. 

Tlie  fat-splitting  enzyme  of  the  pancreatic  juice  is  known  as 
stnipsin  or  lijxtsr.  It  acts  l»y  i-ausini;  neutral  fat.s  to  underjro 
iivdrolvsis,  which  results  in  their  clcava.i^e  into  irlycerinc  and  a  free 
fattv  aciil.  It  was  formerly  thought  that  only  a  portion  of  the  fat 
was  thus  changed,  and  tliat  the  fatty  acid  was  united  to  some  of 
I  he  hases  present  iii  the  |)ancreatic  juice,  forming  a  soap  and 
I'lnulsifying  the  remainder  of  the  fat,  which  was  then  absorbed  as 
line  globules.  Recently  another  view  has  become  prominent, 
which  su})poses  all  the  fat  to  be  converted  into  soluble  glycerine 
and  fattv  acids  which  are  absorbed  as  such  and  later  recombiued 
as  neutral  fats  in  a  tine  state  of  emulsion  called  molecular  fat. 

BILE. 

The  constituents  of  bile  are  partly  excretions  and  partly  secre- 
tions. The  quantity  formed  a  day  in  man  is  from  500  to  <S00  c.c. 
It  consists  of  water,  salts,  bile-pigments,  bile-acids,  cholesteriu, 
lecithin,  neutral  fats,  soaps,  traces  of  urea,  and  a  mucilaginous 
nucleo-al])umin  wrongly  called  mucin.  The  color  of  bile  in  car- 
nivora  is  a  bright  golden  red,  due  to  the  pigment  bilirubin,  while 
in  her])ivora  it  is  green  as  the  result  of  the  pigment  biliverdin. 
Phe  color  of  the  human  bile  varies  from  a  yellow  to  a  dark  olive. 
It  is  feebly  alkaline,  and  has  a  specific  gravity  of  1010  to  1().')0. 
JJilirrrilin  (C,kH,„N.,0,)  is  an  oxidation  product  of  bilirubin 
(CibHisN^Os).  They  are  detected  by  Gmelitis  reaction,  which 
consists  in  bringing  the  solution  to  be  tested  in  contact  with  fum- 
iiifj  iiifrie  arid,  when  a  series  of  color  changes  result.  The  bile- 
pigments  originate  in  the  liver  from  h:emoglobin.  They  are 
mixeil  with  the  food  in  its  ])assage  along  the  intestine,  and  are 
])arlly  real)S()rbe<l  and  carried  back  to  the  liver  in  the  ])ortal 
Mood.  The  bile-acids  are  found  as  the  sodium  salts  of  r////('7K7/o/(> 
and  fdurorholir  acid.  Both  are  present  in  human  ])ile.  and  may  be 
detected  by  Petfenkofera  reaction,  which  consists  in  adding  to  the 
li(piifl  to  be  tested  a  few  drops  of  a  10  per  cent,  solution  of  cane- 
sugar,  and  then,  carefully,  strong  suljjhuric  acid.  The  temjiera- 
ture  must  be  kept  lielow  70°  F.  If  bile-salts  are  pre.sent,  a  violet 
ring  is  fornuMl  at    the  junction  of  the  licjuids,  which  is  due  to  the 


64  DIGESTION. 

formation  of  a  substance  known  as  fiirfurol.  The  latter  reacting 
with  the  bile-salts  gives  the  color.'  The  bile-salts  are  reabsorbed, 
partially  at  least,  and  again  given  off  by  the  liver.  The  value 
of  this  process  is  not  known  unless  it  is  to  economize  material, 
since  the  bile-salts  serve  to  hold  the  excretion  cholesterin  in  solu- 
tion, which  is  constantly  present  in  the  bile,  and  serve  also  to  assist 
in  the  absorption  of  fats  from  the  intestine.  GJiolesterin  (C27H46O) 
is  eliminated  by  the  liver-cells  and  remains  unchanged  in  the 
faeces.  It  is  a  crystallizable,  insoluble  substance,  found  particu- 
larly in  the  medullary  substance  of  nerve-fibres.  The  nucleo- 
albumin  of  the  bile  is  formed  by  the  cells  of  the  ducts  and  gall- 
bladder, and  gives  to  bile  its  mucilaginous  character.  Bile  has 
feeble  antiseptic  powers,  and  to  some  extent  retards  putrefactive 
changes  in  the  intestine,  and  it  also  neutralizes  the  acid  chyme 
from  the  stomach. 

INTESTINAL  SECRETION. 

The  intestinal  secretion,  or  succus  entericus,  may  be  obtained 
by  the  Thirij-  Vella  fistula,  which  is  made  by  cutting  out  a  portion 
of  the  intestine  and  bringing  the  cut  ends  to  the  abdominal  wall, 
so  as  to  form  two  openings.  It  is  a  yellowish  liquid  of  alkaline 
reaction,  having  no  influence  on  proteids  and  fats,  but  may  con- 
vert starches  to  maltose  and  dextrin,  invert  cane-sugar  to  dextrose 
and  levulose,  and  change  maltose  to  dextrose.  This  shows  the 
presence  of  amylolytic  and  inverting  enzymes.  The  latter  is 
called  invertase. 

SECRETION  OF  LARGE  INTESTINE. 

This  secretion  is  composed  mainly  of  mucus,  is  scanty,  alkaline 
in  reaction,  and  has  no  enzymes  of  its  own.  Digestive  changes 
occur,  however,  for  some  time,  and  are  due  to  enzymes  brought 
down  from  above.    Extensive  bacterial  decomposition  takes  place. 

Bacteria  may  be  found  in  any  portion  of  the  intestinal  tract. 
It  has  been  ascertained  that  the  ileum,  at  its  junction  with  the 
colon,  is  acid  after  a  mixed  diet.  This  is  due  to  acetic  acid  (0.1 
per  cent),  which  is  formed  through  the  action  of  bacteria.  In 
the  large  intestine  bacterial  decomposition  results  in  the  forma- 
tion of  many  substances.  Some,  like  skatol,  carbon  dioxide,  hy- 
drogen sulphide,  etc.,  promote  movements  of  the  intestine ;  some, 


6T.1/.1/.I/M    or  Dici.sTioy.  65 

like   plu'iiol    ami   imlol.  an-   rr:il)>url)t'«l,   to   he  eliniinatcfl   in   the 
urine. 

Faeces. — The  t'n.'ee,s  vary  in  eoinpositioii  and  amuunt  with  the 
nature  auil  tlie  (luantity  of  the  food.  Uu  a  mixed  diet  tiie  amount 
in  tweuty-four  hours  varies  from  100  to  500  grammes  in  weight. 
Its  eonstituents  are  indige.>^til)le  materials,  undigestetl  food-stuHs, 
inte.>:tinal  secretions,  products  of  l)aeterial  action,  chole.sterin,  ex- 
cretin,  mucus,  piirment,  salt.s  gases,  and  micro-organisms.  Among 
the  products  of  bacterial  action  are  indol  (C«H;N)  and  ahitit' 
(C,H.,N),  which  are  crystallizahle  bodies  giving  odor  to  the  ficces. 
The  color  is  due  to  lii/drobillrnhin. 

SUMMARY  OF  DIGESTION. 

Proteid  food  is  hut  slightly  altered  in  the  mouth,  and  only  in  a 
mechanical  way.  The  muscle-tibres  of  meat,  for  instance,  are 
iTUshed,  anil  their  connective-tis.sue  sheaths  broken  by  the  action 
of  the  teeth,  thus  becoming  somewhat  white  in  appearance.  Mixed 
with  saliva,  which  has  no  digestive  action  on  these  food-stuHs, 
they  are  passed  into  the  stomach  and  brought  under  the  intluence 
of  the  gastric  juice.  By  the  combined  action  of  the  hydrochloric 
acid  and  the  ferment  pejwin  proteids  pass  through  a  series  of 
steps  which  consist  es.<eiitially  of  a  taking-up  of  water  and  a  break- 
ing into  simpler  bodies.  Syiitoiiin,  the  fii-st  product  formed,  be- 
comes converted  into  proto-  and  hetffropmteose.  These  in  turn  are 
further  changed  to  deuteroprofeoses  and  to  pejifonc^.  But  the 
food  does  not  remain  in  the  stomach  long  enough  for  all  the  pn)- 
teids  to  be  changed  to  peptones.  Some  pass  through  entirely  un- 
changed, while  others  have  reached  various  stages  of  digestion. 

In  the  intestine  the  energetic  action  of  the  trypsin  changes  those 
proteids  that  reach  it  more  quickly  to  peptones  than  the  ga.stric 
juice,  the  intermediate  stage  of  the  primary  proteoses  being 
omitted.  Furthermore,  of  the  peptones  (ampJiopepfoiies),  the 
hemi-  group  is  still  further  changed  to  comparatively  simple 
itmido-bodiei  and  iiltrofjrnon.-^  hii-<e.<.  The  most  important  of  these 
are  leucin  and  tyrosin.  Finally,  in  the  large  intestine  proteids 
that  still  remain  are  attacked  and  decomjX)sed  by  bacteria,  but 
some  escape  and  are  ejec-ted  in  the  fieces. 

Albuminoids. — These  bodies  undergo  changes  analogous  to  those 
of  proteids  ;  the  convei"sion  in  the  stomach  reaches  chiefly  only 

5— Phys. 


66  DIGESTION. 

the  gelatose  stage,  but  the  pancreatic  juice  produces  gelatine  pep- 
tones. 

Carbohydrates. — The  time  that  starches  remain  in  the  mouth  is 
too  short  for  the  ptyalin  of  the  saliva  to  produce  any  very  great 
changes,  and  though  the  digestion  may  continue  for  some  time 
within  food-boli  in  the  stomach,  it  probably  does  not  pass  the 
initial  stages.  The  acidity  of  the  gastric  juice  soon  stops  all  car- 
bohydrate digestion,  and  it  is  not  until  the  food  reaches  the  in- 
testine that  the  amylopsin  of  the  pancreatic  juice  actively  begins 
the  conversion  of  starches.  The  action  of  ptyalin  and  amylopsin 
is  identical.  Starch  is  modified  into  soluble  starch,  and  then  begin 
a  series  of  hydration  changes  during  which  the  starch  molecule  is 
split  into  maltose  and  erythrodextrin.  The  latter  again  into  mal- 
tose and  achroodextrin ;  achroodextrin  again  into  maltose  and  a  still 
simpler  dextrin,  and  so  on  until  only  maltose  results.  In  the  in- 
testinal secretion  there  is  an  enzyme  which  aids  amylopsin  in  the 
conversion  of  starch  to  maltose.  The  sugars  thus  formed  and 
others,  eaten  as  such,  are  by  means  of  inverting  enzymes  (inver- 
tase  and  maltase^  of  the  intestine  changed  to  monosaccharides. 
This  is  illustrated  by  the  following  equations : 

C12H22O11  +  H2O  =  C6H12O6  -p-  C6H12O6 

Maltose.  Dextrose.         Dextrose. 

CiaHaaOn  +  H2O  =  CgHiaOg  +  CgHijOg 
Cane-sugar.  Dextrose.  Levulose. 

It  has  been  found  that  cane-sugar  may  also  be  converted  to 
dextrose  and  levulose  in  the  stomach.  Carbohydrates  that  escape 
digestion  and  absorption  and  reach  the  large  intestine  are  largely 
destroyed  by  bacteria. 

Fats. — These  are  not  changed  until  they  reach  the  fat-splitting 
ferment,  steapsin,  of  the  pancreatic  juice,  except  that  they  are 
separated  from  the  connective  tissue  by  the  action  of  the  teeth  and 
proteolytic  enzymes,  and  are  partially  melted  by  the  heat  of  the 
body  in  the  stomach.  In  the  intestine  fats  are  changed  to  glycerine 
and  a  corresponding  fatty  acid.  The  latter  may  unite  with  bases 
present  to  form  soaps,  which  emulsify  the  remaining  unaltered  fat. 
According  to  one  view,  fat  is  mainly  absorbed  in  the  form  of  an 
emulsion.  According  to  another  and  later  view,  the  greater  part 
is  converted  to  fatty  acid  and  glycerine,  absorbed  as  such,  and 
then    recombined    to  form   neutral  fat.     While  considering  the 


SELF-DIGESTION  OF   THE  SToMAdl.  »i7 

action  of  digestive  juices,  it  is  interesting  and  important  to  renieni- 
lier  that  tlie  ferment  rennin  of  the  gastric  juice  ctKKjiilutvx  milk. 
The  casein  of  the  milk  under  the  influence  of  the  enzyme  under- 
goes a  hyilrolytic  cleavage,  with  the  formation  of  paracasein  and 
whcy-proteid.  Paracasein  unites  with  calcium  to  form  the  insolu- 
l)le  t'urd.  Till'  action  of  rennin  is  coniined  to  milk,  and  the  value 
of  the  curtlling  action  lies  prol)al)ly  in  an  easier  conversion  of  the 
milk  protcids  in  the  coagulated  i'onii.  The  digestion  of  milk  after 
i-oagulation  is  carried  ou  by  the  enzymes  of  the  gastric  and  pan- 
creatic juices. 

SELF-DIGESTION  OF  THE  STOMACH. 

Why  the  stomach  or  any  other  portion  of  the  intestinal  tract 
brought  into  contact  with  digestive  juices  is  not  destroyed  has 
given  ri.<e  to  much  discu.<sion.  Normally,  self-digestion  does  not 
occur,  but  if  an  animal  is  killed  while  in  full  digestion  and  the 
body  is  ke])t  warm,  the  stomach  will  be  destroyed.  This  has  been 
found  to  take  place  in  human  bodies.  If  a  portion  of  the  stomach 
is  deprived  of  its  blood-supply,  that  portion  will  l)e  attacked  and 
a  perforation  of  the  stomach  may  result.  The  inunuuity  of  the 
stomach  to  the  gastric  juice  has  been  explained  in  a  nund)er  of 
wavs  but  not  satisfactorily.  li  has  been  said  that  the  epithelial 
lining  of  the  stomach  jjrevents  the  a])S(jrption  of  the  gastric  juice, 
but  this  explanation  raises  the  question  why  the  living  epithelial 
cells  are  immune. 

The  secretion  of  mucus  forming  a  protective  coating  for  the 
.«tomach  is  an  inadequate  explanation,  owing  to  the  difficulty  of 
conceiving  such  a  means  of  protection  to  be  as  perfect  as  it  is. 
Another  theory  which  holds  the  alkaline  blood  to  neutralize  the 
acid  of  the  stomach  as  it  is  formed  cannot  ])e  a))])lied  in  the  case 
of  the  intestine,  where  the  digestive  juice  is  alkaline.  An  ex- 
planation is  at  ])resent  impossible.  All  that  can  be  said  is  that 
the  immunity  of  the  intestinal  tract  is  due  to  the  i'act  that  it  is 
alive.  Bernard  introduced  the  hind-leg  of  a  living  frog  into  a 
dog's  stomach  tli rough  a  fistula.  It  was  digested.  But  in  this 
case  the  cells  of  ilic  frog's  lind)  were  first  destroyed  by  the  acid. 
It  has  been  shown  by  Neumeislcr  that  a  living  frogs  leg  is  not 
digested  by  a  strong  pancreatic  digestive  nuxture  of  weak  alkaline 
reaction,  because  in  this  ea.-Je  the  cells  are  not  killed. 


68 


DIGESTION. 


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70  DIGESTION. 


QUESTIONS  ON  CHAPTEE  III. 

What  is  digestion  ? 

What  are  food-stuflfs?     Give  classes. 

Into  what  subdivisions  do  simple  proteids  fall  ? 

How  are  globulins  separated  from  albumins? 

How  are  peptones  isolated  from  other  proteids  ? 

What  purposes  do  peptones  serve  ? 

What  can  be  said  of  the  molecular  structure  of  proteids  ? 

Give  tests  for  the  identification  of  proteid. 

How  do  albuminoids  resemble  proteids? 

In  what  way  are  they  like  carbohydrates  ? 

What  are  the  main  groups  of  carbohydrates  ?    Examples. 

How  may  dextrose  be  detected  ? 

What  is  the  test  for  cane-sugar  ? 

What  chemical  is  used  for  the  detection  of  starch? 

How  do  fats  compare  with  carbohydrates  as  a  source  of  energy? 

What  is  saponification  ? 

Of  what  value  are  water  and  salts  to  the  body  ? 

In  what  sense  may  oxygen  be  called  a  food  ? 

What  are  the  characteristics  of  enzymes  ? 

In  what  ways  are  enzymes  supposed  to  act  ? 

How  are  enzymes  classified  ? 

Describe  the  saliva.     What  is  its  composition? 

What  is  the  function  of  saliva  ? 

Give  detailed  steps  of  the  action  of  ptyalin  on  starch. 

What  is  the  action  of  acid  on  the  activity  of  ptyalin  ? 

Why  is  starch  more  easily  digested  when  cooked  than  when  raw  ? 

Describe  the  gastric  juice. 

What  are  the  proofs  that  the  acid  of  the  gastric  juice  is  free  hydrochloric 
acid? 

How  is  the  reaction  of  the  blood  and  the  urine  affected  during  active  secre- 
tion of  gastric  juice? 

What  is  pepsin  ? 

Give  detailed  steps  of  the  action  of  hydrochloric  acid  and  pepsin  on  proteids. 

Explain  the  action  of  the  ferment  rennin  in  detail. 

Describe  the  curd  of  human  milk. 

In  what  ways  are  fats  and  albuminoids  changed  in  the  stomach  ? 

Where  does  the  food  undergo  its  greatest  digestive  changes? 

Describe  the  pancreatic  juice.     Its  composition. 

How  does  the  action  of  trypsin  diflfer  from  that  of  pepsin  ? 

What  are  amphopeptones? 

What  is  the  source  of  leucin  and  tyrosin  ? 

Compare  the  action  of  amylopsin  and  ptyalin. 

What  is  lipase  ? 

What  is  the  action  of  steapsin  on  fat  ? 

Describe  the  bile. 

What  causes  the  diflPerence  of  the  color  in  the  bile  of  herbivora  and  car- 
nivora  ? 

How  are  the  bile-pigments  detected  ? 

What  is  the  source  of  the  bile-pigments? 

What  is  their  fate  ? 

What  are  bile-acids  ?    How  detected  ? 

Give  fate  of  bile  acids.     What  is  their  function? 


MASTICATFON— DEGLUTITION.  71 


Doscrilio  cholestoriii. 

W'liat  inakfs  the  hile  viscid  ? 

I  low  is  tlu'  iiit<-stin:il  secretion  obtained  Y 

Describe  the  siicciis  eiilericns. 

|)escril)e  the  secretion  of  tlic  lar^o  intestine. 

What  is  tlic  reaction  of  the  hirge  intestine? 

Wiiat  is  the  reaction  due  to? 

Wiiat  ciiannes  do  bacteria  produce  in  the  intestine? 

Describe  tiie  t'lecos. 

What  substances  give  odor  and  color  to  the  fceces? 


ClIAPTEK    IV. 
MUSCULAR  MECHANISMS. 

MASTICATION. 

In  ofder  that  the  food  iniiy  reailily  be  swallowed  and  acted 
UjX)!!  hy  the  diire.^tive  juices  it  is  finely  divided  hy  the  action  of 
the  juws,  which,  by  means  of  the  incisors  and  canines,  cut  the 
fooil,  ami  by  means  of  the  bicuspids  and  molars,  crush  it.  The 
lower  jaw  is  raised  by  the  mtisseter,  temporal,  and  internal  ptery- 
goid muscles  ;  depression  is  largely  passive,  but  is  aided  by  the 
digji-^trics  and  slightly  by  the  mylohyoid  and  geniohyoid  muscles. 
When  the  infrahyoid  group  fix  the  hyoid  lione,  all  the  muscles 
])assing  between  it  and  the  mandible  act  to  depress  the  latter  ;  it 
is  movetl  laterally  by  the  external  pterygoids  acting  separately, 
and  forward  by  their  joint  action,  and  is  retracted  by  the  hori- 
zontal fibres  of  the  temporals.  The  action  is  voluntary,  the 
impulses  coming  through  the  trigeminal  and  hypoglossal  nerves. 
The  tongue  and  chocks  servo  to  liring  and  keep  the  food  between 
the  teeth. 

DEGLUTITION. 

This  process  is  usually  diviiled  into  tlirrr  affir/ra : 

1.  The  food  is  pro]ierly  j)laced  on  the  tongue,  which  is  e1ovato(l 
against  the  palati'  from  tip  to  base,  forcing  the  food  toward  the 
fauces. 

2.  The  food  is  rapidly  transferred  through  the  pharynx  by  the 
contraction  of  the  tongue  and  pharyngeal  muscles,  while  simul- 
taneously all  ])assages  with  the  exception  of  that  to  the  a^so|)hagus 
are   closed.      The    mouth   cavitv    is  shut  off   bv    the   tonuue    and 


72  MUSCULAR  MECHANISMS. 

anterior  pillars  of  the  fauces ;  the  nasal  cavity  by  the  soft  palate, 
posterior  pillars  of  the  fauces,  and  uvula ;  the  larynx  by  the 
depression  of  the  epiglottis,  adduction  of  the  cords,  and  elevation 
of  the  larynx  under  the  base  of  the  tongue. 

3.  Having  reached  the  oesophagus,  the  food  is  seized  by  the 
circular  muscles,  which  contract  from  above  downward  in  the  form 
of  a  peristaltic  wave.  The  most  active  contraction  is  just  above 
the  bolus  of  food.  The  total  time  involved  by  the  food  in  reaching 
the  stomach  is  about  six  seconds.  Liquids  when  in  the  second 
stage  are  brought  under  pressure  by  the  contraction  of  the  mylo- 
hyoid and  hyoglossi  muscles,  and  quickly  shot  deep  down  into  the 
oesophagus.  Deglutition  is  a  reflex  act,  with  the  exception  of  the 
first  stage.  Section  of  the  oesophagus  does  not  prevent  the  passage 
of  the  peristaltic  wave.  The  afferent  fibres  are  in  branches  of 
the  fifth,  ninth,  and  tenth  nerves  (especially  in  the  superior  laryn- 
geal branch  of  the  tenth).  The  centre  in  the  medulla  is  not  defi- 
nitely localized.  The  efferent  fibres  are  in  the  fifth,  seventh 
(ninth),  tenth,  and  twelfth  nerves. 

MOVEMENTS  OF  THE  STOMACH. 

When  food  is  passed  into  the  stomach  it  is  moved  about  and 
thoroughly  mixed  with  the  gastric  juice  for  several  hours,  while 
at  regular  intervals  peristaltic  waves  sweeping  over  the  organ  force 
some  of  the  digested  mass  through  the  relaxed  pyloric  sphincter 
into  the  intestine.  The  peristaltic  waves  begin  feebly  in  the  fundic 
end  of  the  stomach,  and  increase  in  intensity  until  they  reach  a 
maximum  at  the  transverse  band,  which  contracts  so  markedly  as 
to  divide  the  stomach  into  two  portions.  Then  follows  a  contrac- 
tion of  the  antrum  upon  the  food  that  has  been  moved  into  it, 
forcing  the  digested  portions  into  the  duodenum.  Portions  not 
digested  set  up  an  antiperistaltic  wave  and  are  throwai  back  into 
the  fundus.  Throughout  the  digestion  of  the  food  the  fundus  is  in 
a  tonic  state  and  gradually  contracts  to  smaller  dimensions  as  the 
food  disappears.  The  peristalsis  of  the  stomach  is  independent  of 
the  nervous  system.  There  is,  however,  a  rich  supply  of  nerve- 
fibres  from  two  sources :  from  the  vagi  and  from  the  solar  plexus. 
Stimnlation  of  the  first  causes  a  contraction,  and  stimulation  of  the 
second  an  inhibition,  of  the  stomach.  Their  function  is  probably 
a  regulatory  one. 


VOMlTISa-MoVKMEyTS  OF   THK   IXTESTfXKS.        73 

VOMITING. 

Vomitiiii;  i.s  a  coinplcte  rrjjcr  action.  It  is  preceded  hv  a  feel- 
iii<;  of  nausea,  a  flow  of  saliva,  and  retcliiiiLT  nioveinenis  which  are 
l)rouirlit  about  hy  spasmodic  contractions  of  the  diaphra;_Mn  with  a 
clos;.'d  <,dottis.  This  causes  the  nejj^ative  pressure  in  the  thorax  to 
increase  and  open  the  a'sophagus,  while  simultaneously  jtressttre  is 
hroucfht  to  hear  upon  the  utoinach.  The  abdominal  muscles  vijior- 
ously  contractiuiT  force  the  contents  out  of  the  cardiac  end  of  the 
stomach  and  up  throuirh  the  mouth.  The  glottis  is  closed,  and  the 
nasal  passages  also,  llie  xfomacli  duriiuj  vomilliKj  inaij  not  be  ui- 
aclive,  hut  tlir  main  factor  in  the  ejection  of  itx  content-*  is  the  con- 
traction of  the  ahdnmina/  muscles.  This  was  shown  1)V  Mageudie, 
who  substituted  a  ])ladder  of  water  for  the  stomach  and  produced 
vomiting  by  injection  of  an  emetic.  It  has  been  shown,  moreover, 
that  an  emetic  is  without  effect  in  a  curarized  animal.  Vomiting 
is  brought  about  by  local  irritation  of  the  mucous  membrane  of 
the  stomach,  by  tickling  the  })harynx,  by  psychical  states,  lesions 
of  the  brain,  by  toxic  sub.stances  in  the  blood,  etc.  The  afferent 
path  when  the  retlex  is  from  the  stomach  is  through  the  vagus.  A 
centre  has  been  described  near  the  calamus  scriptorius,  but  its 
existence  is  not  certain.  The  efferent  impulses  pass  over  fibres  of 
the  vagus,  phreuics,  and  spinal  nerves  that  supply  the  abdominal 
muscles. 

MOVEMENTS  OF  THE  INTESTINES. 

These  are  of  the  same  nature,  but  simpler  than  those  of  the 
stomach.  There  are  two  kinds — the  jierisfalfic  and  the  rhtithmic. 
Peristal'^is  is  effected  mainly  through  a  contraction  of  the  circular 
muscle-fil)res  of  the  intestine,  which  involves  successive  portions 
and  is  followed  by  a  gradual  relaxation  in  the  same  order.  This 
gives  rise  to  a  series  of  waves  that  normally  pass  from  the  stomach 
to  the  rectum.  Waves  in  the  reverse  direction  are  known  as  anti- 
peristaltic. That  peristalsis  is  due  to  some  mechanism  in  the  walls 
of  the  intestine  lias  been  shown  by  cutting  out  a  portion  and  re- 
placing it  in  a  reversed  position.  Sucli  animals  show  nutritive 
ilisturitances  and  examination  reveals  an  accumulation  of  food  at 
the  upper  end  of  the  reversed  part.  The  peristaltic  waves  pa.ss 
over  the  intestine  normally  quite  slowly,  but  almormal  waves  may 
.sweep  over  its  entire  length  in  a  minute. 


74 


MUSCULAR  MECHANISMS. 
Fig.  4. 


Diagram  to  illustrate  the  nerves  of  the  alimentary  canal  in  the  dog  (Foster).  The 
figure  is,  for  the  sake  of  simplicity,  made  as  diagrammatic  as  possible,  and  does  not 
represent  the  anatomical  relations.  Oe.  to  Ret.  The  alimentary  canal,  CBSophagus, 
stomach,  small  intestine,  large  intestine,  recrum.  L.  V.  Left  vagus  nerve,  ending 
on  front  of  stomach,  r.l.  Recurrent  laryngeal  nerve  supplying  upper  part  of  oesoph- 
agus. R.  V.  Right  vagus,  joining  left  vagus  in  oesophageal  plexus,  oe.pl.,  supplying 
posterior  part  of  stomach  and  continued  as  R'.  V.  to  join  the  solar  plexus,  here  rep- 
resented by  a.  single  ganglion  and  connected  with  the  inferior  mesenteric  ganglion  (or 
plexus)  m.gl.  a.  Branches  from  the  solar  plexus  to  stomach  and  small  intestine  and 
from  the  mesenteric  ganglion  to  the  large  intestine.  Spl.  maj.  Large  splanchnic 
nerve  arising  from  the  thoracic  ganglia  and  rami  communicantes,  r.c.,  belonging  to 
dorsal  nerves  from  the  sixth  to  the  ninth  (or  tentla).  Spl.  min.  Small  splanchnic 
nerve  similarly  arising  from  tenth  and  eleventh  dorsal  nerves.  The.'-e  both  join  the 
solar  plexus  and  thence  make  their  way  to  the  alimentary  canal,  c.r.  Nerves  from 
the  ganglia,  etc.,  belonging  to  eleventh  and  twelfth  dorsal  and  first  and  second 
lumbar  nerves,  proceeding  to  the  inferior  mesenteric  ganglia  (or  plexus),  m.  gl.,  and 
thence  by  the  hypogastric  nerve,  n.  hyp.,  and  the  hypogas'tric  plexus,  pi.  hyp.,  to  the 
circular  muscles  of  the  rectum,  l.r.  Nerves  from  the  second  and  third  sacral  nerves, 
S.2,  ,S'.3  (nervi  erigentes),  proceeding  by  the  hypogastric  plexus  to  the  longitudinal 
muscles  of  the  rectum. 


DEFECA  TION- MICTURITION.  7  5 

The  rhythmic  movements  are  caused  by  the  contractions  of  the 
circular  muscles  over  extensive  portions  of  the  intestine  at  the 
same  time.  By  pressin*,'  ujjon  the  veins  of  the  submucous  plexus 
they  f(U'ce  the  blood  into  the  superior  mesenteric  vein,  and  so  aid 
ill  maintaininir  a  circulation  tlirouL''h  the  intestines.  These  move- 
ments dili'er  from  peristalsis  in  not  beinj^  prevente(l  bv  iiicotin,  iu- 
dicatinic  a  })urely  nniscular  nature. 

The  intestines  have  a  douhlf  Nfrve-supply.  The  fibres  of  the 
vagi  carry  chietly  viator  impulses,  while  those  of  the  sympathetic, 
chiefly  inhibitory  impulses.  The  intestinal  movements  are  not 
altered  by  complete  severance  of  all  extrinsic  fibres,  so  that  the 
latter  probably  have  only  a  regulatory  influence.  It  is  known 
that  the  movements  may  l)e  influenced  by  psychical  states,  so  that 
there  are  evidently  connections  with  higher  centres. 

DEFECATION. 

When  the  undigested  food  has  reached  the  lower  part  of  the 
large  intestine  and  the  rectum,  sensory  impulses  pass  to  the  brain 
from  the  latter,  giving  rise  to  a  desire  to  defecate.  The  normal 
peristaltic  movements  of  the  rectum  are  increased,  while  volunta- 
rily a  deep  breath  is  taken,  the  glottis  is  closed,  and  pressure  is 
brought  to  bear  upon  the  abdominal  contents.  The  external 
sphincter  ani  is  voluntarily  relaxed,  while  the  internal  sphincter  is 
inhibited.  Both  rectum  and  sphincters  have  a  double  nerve-sup- 
])ly,  which  in  function  are  motor  and  inhibitory.  It  has  been 
shown  that  scctit)n  of  the  spinal  cord  of  dogs  in  the  lower  thoracic 
region  does  not  prevent  normal  defecation.  The  ctittrv  probablv 
lies  in  the  lumbar  cord,  but  is  connected  with  the  brain  so  as  to  be 
under  voluntary  control. 

MICTURITION. 

The  urine  as  it  is  formed  in  the  kichiev  is  periodicallv  carried 
to  the  bladder  by  a  peristaltic  action  of  the  ureters.  AN'licther  the 
pt'Hstalsis  is  due  to  the  stimulus  of  the  contained  urine  or  whether 
the  ureters  are  automatically  rhythmic  is  not  known.  The  urine 
is  emptied  into  the  bladder  in  a  series  of  spurts,  and  is  prevented 
from  flowing  through  the  urethra  by  the  elasticity  of  the  ])arts  and 
perhaps  al.so  by  a  tonic  contraction  of  the  internal  s])hincter  of  the 
bladder.     As   it  increases  in   amount   and  a  desire  to  micturate 


76  MUSCULAR  MECHANISMS. 

arises,  the  sphincter  of  the  urethra  is  voluntarily  contracted  to 
prevent  the  escape  of  urine,  and  the  back-flow  through  the  ureters 
is  prevented  by  their  oblique  entrance.  Micturition  is  initiated 
voluntarily  by  a  relaxation  of , the  sphincter  urethrse.  The  walls 
of  the  bladder  contract,  driving  the  liquid  out  forcibly.  This  may 
be  aided  by  a  closure  of  the  glottis  and  a  contraction  of  the  abdom- 
inal muscles.  In  the  male  the  last  portions  are  ejected  in  spurts 
by  the  contractions  of  the  bulbocavernosus  muscle.  The  totie  of 
the  bladder  is  continually  undergoing  changes,  so  that  the  pressure 
of  the  urine  varies  independently  of  the  quantity  present.  This 
explains  why  a  desire  to  micturate,  if  not  satisfied,  may  pass  off. 
The  centre  of  micturition  has  been  located  in  the  lumbar  portion 
of  the  cord,  between  the  second  and  fifth  lumbar  spinal  nerves. 
The  bladder  has  a  double  nerve-supply  : 

1.  From  lumbar  nerves  passing  through  the  inferior  mesenteric 
ganglion  and  hypogastric  nerves.  Stimulation  of  these  causes  a 
feeble  contraction. 

2.  From  sacral  spinal  nerve-fibres  contained  in  the  nervus  eri- 
gens.     Stimulation  of  these  causes  a  strong  contraction. 

PARTURITION. 

This  process  is  inaugurated  by  painless,  rhythmical  peristaltic 
waves  that  sweep  over  the  upper  segment  of  the  uterus.  These 
contractions  increase  in  intensity  and  duration  until  they  give 
pain,  which  is  intensified  by  resistance  ahead  or  may  be  absent 
altogether  if  the  child  is  small  and  the  canal  large  and  free.  The 
pain  is  at  first  confined  to  the  uterus,  but  later  spreads  up  into  the 
abdomen  and  down  into  the  thighs.  Contractions  in  the  human 
being  involve  only  the  upper  portions  of  the  uterus,  the  lower 
segment  and  cervix  remaining  passive.  When  the  membrane 
which  precedes  the  foetus  in  its  passage  through  the  os  uteri 
bursts,  there  is  for  a  time  a  cessation  of  uterine  contractions  (owing 
to  the  considerable  reduction  in  the  bulk  of  the  uterine  contents), 
but  they  are  soon  renewed  with  increased  vigor,  aided  by  forcible 
contractions  of  the  abdominal  muscles  and  by  forcible  expirations 
with  closed  glottis.  By  these  means  the  head  of  the  foetus  is 
gradually  pushed  through  the  os  into  the  vagina,  followed  by  the 
more  easily  passing  remainder  of  the  body.  After  expulsion  of 
the  foetus  the  contractions  gradually  diminish,  becoming  painless, 


LOCOMOTOR  MECHANISMS.  77 

and  in  al)ont  fifteen  minutes  the  nfter-hirtli,  consiytinjr  of  plaeontu, 
amnion,  ehorion,  deeitlua  rellexa,  and  parts  of  the  decidua  vera 
apj)ear!?.  At  tliis  time  the  blood  Hows  freely  ;  the  average  loss, 
amoiintint,'  to  about  400  grammes,  which  can  be  and  should  be 
greatly  reduced  by  a  proper  "following  tlown  " — i.e.  intermittent 
massage — of  the  fundus.  After  parturition,  by  a  process  of  involu- 
tion lasting  for  several  weeks,  the  uterus  returns  to  its  unimpreg- 
nated  state.  The  entire  process  is  a  irjlex  act,  the  nervous  mitre 
being  in  the  lumbar  portion  of  the  cord.  The  nerves  reach  the 
uterus  iu  company  with  blood-vessels,  and  are  derived  from  the 
pelvic  plexus. 

LOCOMOTOR  MECHANISMS. 

The  two  iiundred  or  more  bones  of  the  body  are  joined  together 
to  ibrm  articulations  of  four  types  :  sutureii,  symphyses,  syiidesmoses, 
and  (//(</•/// /•ox'.s'. 

A  suture  is  formed  when  two  bones  gradually  interlock  immov- 
ably, leaving  only  a  mere  or  less  distinct  seam.  The  best  exam- 
ples are  in  the  skull. 

A  sy7n/)hysis  is  the  union  of  two  boues  by  fibrocartilage,  as  in 
the  ca^se  of  vertebrre.     This  allows  a  limited  amount  of  movement. 

A  .^}i)i(h'.'^wo.'<!.-<  is  a  union  of  two  bones  by  fibrous  bauds  which 
allows  considerable  movement  as  in  the  inferior  til)iofil)ular  artic- 
ulation. 

A  fliarthrosls  is  a  uinon  between  two  bones  that  allows  the 
greatest  movement,  generally,  however,  only  in  a  special  direction. 
The  parts  in  contact  are  lined  with  cartilage,  and  lubricated  with 
a  viscid  synovial  fluid.  The  union  is  made  firm  by  guiding  liga- 
ments and  fibrous  capsules.  In  some  cases,  as  in  the  head  of  the 
femur  and  acetabulum,  the  parts  fit  so  well  that  they  are  kept  in 
place,  partially,  at  least,  by  atmos])heric  pressure. 

The  morP7nentx  brfirrrn  jninfs  maybe:  (1)  Aiu/iilar  ;  (2)ot'clr- 
cumihicflon  ;  (o)  of  rot(ifi(ni ;  (4)  </!!(lln(i.  In  the  first  the  angle  be- 
tween the  long  axis  of  the  bones  changes  in  value.  In  the  second 
the  longitudinal  axis  of  the  bone  forms  the  sides  of  a  cone  whose 
apex  is  at  the  joint.  In  the  third  the  bone  moves  about  its  longi- 
tudinal axis.     In  the  fourth  one  bone  slides  over  the  other. 

Many  of  the  bones  may  be  looked  upon  as  levers,  with  the  mus- 
cles attached  as  sources  of  power.  Levers  are  divided  into  three 
classes,  according  to  the  relative  position  of  the  power,  the  weight 


78 


MUSCULAR  MECHANISMS. 


to  be  moved,  and  the  axis  of  motion  or  fulcrum.  Different  move- 
ments of  the  foot  offer  an  illustration  of  the  three  kinds  of  levers. 
The  first  kind  (Fig.  5),  where  the  fulcrum  (F)  is  between  the 
source  of  power  (P)  and^  the  weight  of  resistance  (W),  is  shown 
when  the  foot  is  raised  and  the  toe  tapped  upon  the  ground,  the 
ankle-joint  being  the  fulcrum.  The  second  kind  of  lever,  where 
W  is  between  F  and  P,  is  illustrated  when  the  body  is  raised  upon 
the  toes,  which,  resting  upon  the  ground,  are  the  fulcrum.  The 
third  kind  of  lever,  where  P  is  between  F  and  W,  is  illustrated 
when  a  weight  is  held  up  by  the  toes,  the  ankle  being  the  fulcrum 
and  the  anterior  group  of  muscles  of  the  leg  the  source  of  power. 
Standing  is  a  complex  coordinated  action  in  which  the  muscles 
are  continually  in  play  to  keep  the  centre  of  gravity  of  the  body 


Fig.  5. 


I  II 

Illustration  of  levers  of   all  three  orders  (Huxley) ; 
Fulcrum,    P.  Fower. 


Ill 
Weight  of  resistance. 


over  the  base  of  support.  In  xvalking  the  centre  of  gravity  is 
continually  being  put  forward,  but  the  body  is  kept  from  falling 
by  the  legs,  which  alternately  move  forward  to  sustain  it.  One 
foot  or  the  other  is  continually  on  the  ground.  Running  differs 
in  that  the  body  is  more  forcibly  moved  ahead  by  vigorous  pushes. 
The  body  is  more  inclined,  and  both  feet  leave  the  ground  at 
times. 

VOICE. 

The  larynx  is  a  closed  cavity,  except  in  its  communications  with 
the  trachea  below  and  the  pharynx  above.  The  walls  are  made 
up  of  cartilages,  together  with  various  muscles  and  membranes. 
Across  the  cavity  in  an  anteroposterior  direction  are  stretched  the 
vocal  cords  by  the  vibration  of  which  the  voice  is  produced.  Mere 
vibration  of  the  cords  held  in  a  state  of  tension  by  muscular  action 


QUESTIOys   n.V  ClIA  I'lhll    fV.  79 

priHluces  ill  itsi-lt  Imt  a  fV-ehle  sound.  This  is  iiitciisiHctl  hy  rri'n- 
Idireinciit  of  ihe  vilirations  hy  rt'sonating  cavitii'S  above  ami  hclow 
the  cords.  It  is  necessary  to  consider  three  features  of  tlie  voice — 
(he  iiitoislfji,  tlie  ])ifrh,  and  the  (jioi/itij.  The  infnisifi/  depends 
iil)on  the  aniplituile  of  vibrations  of  the  cords.  This  is  partly  the 
result  of  their  structure  and  partly  of  the  eneriry  with  which  the 
air  passes  between  them.  The  j)itch  is  determined  by  the  thick- 
ness, tension,  and  leiiL'th  of  the  cords.  The  (iiidliftj  of  the  tone 
depends  upon  the  i-haracter  of  the  upper  partial  tones  which  are 
combined  with  the  fundamental  tone.  These  are  varied  by  alter- 
inj;  the  shape  and  size  of  the  buccal  and  nasal  cavities.  The 
voice  is  controlled  by  an  exceedingly  complex  nervous  mechanism 
of  afferent  and  etierent  fibres  to  various  centres  in  the  cerebral 
cortex.  That  relations  between  the  hearing  and  speech  centres, 
for  instance,  are  very  intimate  is  shown  by  the  fact  that  dumbness 
is  usually  a  defect  of  hearing  which  leaves  the  voice  uncontrolled 
bv  the  ear  in  pitch  and  (piality.  The  pitch  of  the  voice  is  ele- 
vated usuallv  by  the  contraction  of  the  crico-thyroid  muscle,  which 
stretches  the  vocal  cords.  There  are  numerous  other  methods  of 
altering  the  pitch.  Whenever  there  is  a  transition  from  one 
method  to  another,  a  break  occurs  in  the  musical  scale.  The 
range  of  voice  between  these  breaks  is  known  as  a  rer/isfer.  The 
lowest  register  is  commonly  designated  as  the  chest  I'oice,  and  the 
highest  as.  the  head  voice.  When  a  third  division  is  made,  it  is 
by  some  called  the  falsetto.  Lanr/nar/e  consists  of  short  musical 
sounds  produced  by  the  vocal  cords  with  other  noises  added  by 
the  mouth-parts,  the  whole  being  interrupted  by  ditlerent  methods 
of  obstruction.  In  whispering  the  musical  component  is  greatly 
replaced  by  noisy  vibrations. 

QUESTIONS  ON  CHAPTER  IV. 

What  is  the  function  of  the  jaws  and  the  teeth  ? 

Give  action  of  the  imiscles  concerned  in  mastication. 

What  i)urj)ose  do  the  tonfjiie  and  clieeks  serve? 

Into  what  stages  is  deglutition  divided  ? 

Descrihe  each  stage  in  detail. 

How  does  the  deglutition  of  liquids  difler  from  that  of  solids? 

How  long  does  it  take  food  to  ])ass  from  the  pharynx  to  the  stomach? 

Is  swallowing  reflex  or  voluntary? 

What  is  the  eflect  of  sectioning  the  opsophagus  on  peristalsis? 

Give  the  nervous  mechanism  of  deglutition. 

Describe  the  movements  of  the  stomach. 

What  is  the  function  of  the  fundic  end  of  the  stomach? 


80  ABSORPTION. 

Give  the  nerve-supply  to  the  stomach  and  its  function. 

Describe  vomiting.     Is  it  a  reflex  act  ? 

What  experiment  shows  that  food  is  ejected  from  the  stomach  mainly  by 
abdominal  muscles? 

Give  the  nerves  involved  in  vomiting. 

Explain  the  movements  of  the  intestines. 

What  is  antiperistalsis  ? 

What  is  the  proof  that  normal  peristalsis  is  due  to  a  nervous  mechanism? 

What  are  the  differences  between  the  peristaltic  and  the  rhythmic  move- 
ments of  the  intestine  ? 

How  do  rhythmic  movements  aid  the  circulation  ? 

Discuss  the  nervous  mechanism  of  the  intestines. 

Describe  defecation.     Give  nerve-supply  and  locate  centre. 

Describe  micturition. 

Explain  why  a  desire  to  micturate  may  pass  off. 

Locate  centre  and  give  nerve-supply  involved  in  micturition. 

Describe  parturition. 

What  forms  the  after-birth  ? 

How  much  blood  is  lost  during  parturition  ?     Is  this  essential  ? 

Give  source  of  nerve-supply  and  locate  centre  involved  in  parturition. 

Name  the  types  of  articulations  between  bones. 

Define  each  type. 

What  kinds  of  movements  may  take  place  between  joints? 

Describe  the  three  kinds  of  levers  formed  by  bones. 

Define  standing,  walking,  and  running. 

How  is  the  voice  produced  ? 

Define  pitch,  intensity,  and  quality  of  voice. 

What  is  the  relation  of  the  centre  of  speech  to  other  centres  of  the  cerebral 
cortex  ? 

What  constitutes  a  register? 

Define  head  voice,  chest  voice,  and  falsetto. 

Define  language.     Define  whispering. 


CHAPTER   V. 

ABSORPTION. 


General  Principles. — When  food  in  the  intestinal  canal  has 
undergone  its  digestive  changes,  it  is  absorbed.  The  alimentary 
canal  from  oesophagus  to  rectum  consists  of  a  single  layer  of 
columnar  epithelial  cells  placed  on  a  basement  membrane.  The 
soKible  diffusible  constituents  of  the  food  on  one  side  and  the 
blood  on  the  other  side  seem  to  offer  favorable  conditions  for  fil- 
tration and  osmosis.  But  it  has  been  proved  that  the  activity  of 
the  epithelial  cells  is  an  important  factor  in  absorption. 

1.  Substances  are  absorbed  from  the  intestine  having  the  same, 
less,  or  greater  osmotic  tension. 


ABSORPTION  FROM   TIIP:  SMALL    rNTESTrNH.  81 

2.  Sii<i:ar  and  ju-ptoiK-.'^,  which  are  les.s  tliiriisililc  than  sodium 
sulphate,  are  al)ti()rl)ed  more  rapidly. 

3.  Non-dializal)le  suhstaiicea  like  egg-albumen  may  l)e  absorbed. 

4.  Some  substaiiees  like  peptone  are  changed  in  their  passage 
through  tlie  intestinal  wall. 

There  are  tiro  /ititha  which  altsorhed  {jroduct^^  may  take  :  they 
mav  pa.ss  directly  into  the  blood  of  the  capillaries'  and  so  into  the 
portal  system,  in  which  case  they  arc  taken  to  the  liver,  or  they 
may  jia.ss  into  the  lacteals  of  the  lymphatic  system,  forming  chyle. 
In  this  case  they  pass  through  the  thoracic  duct  to  enter  the  gen- 
eral circulation  at  the  junction  of  the  left  internal  jugular  and 
subclavian  veins.  It  will,  therefore,  be  noted  that  the  blood  is  the 
jinal  objcctice  jioint  by  each  path. 

ABSORPTION  FROM  THE  STOMACH. 

The  absorption  of  substances  from  the  stomach  is  not  very 
marked.  Sugars,  peptones,  and  proteoses  may  be  absorbed  with 
difficulty.  The  same  is  true  of  water,  which  is  usually  rapidly 
passed  into  the  duodenum.  Alcohol  is  absorbed  more  rapidly, 
salts  slowly,  and  tats  not  at  all.  Some  salts  like  sodium  iodide  are 
not  absorbed  at  all  in  dilute  solutions,  but  when  the  concentration 
of  the  solution  reaches  '-^  per  cent.,  absorption  becomes  pronounced. 
Normally,  salts  nevei  reach  this  degree  of  concentration.  It  bas 
been  found  that  the  absorption  of  sodium  iodide  is  greatly  in- 
creased by  mustard,  pepper,  and  alcohol,  which  act  either  by  oon- 
ge.sting  the  mucous  membrane  or  by  stimulating  the  epithelial 
cells  to  greater  activity. 

ABSORPTION  FROM  THE  SMALL  INTESTINE. 

The  food  in  its  passage  along  the  intestine  moves  slowly,  requir- 
ing from  nine  to  twenty-three  hours  after  ingestion  to  a])pear  at 
the  end  of  the  xmall  intestine.  The  latter,  moreover,  presents  a 
vast  surface  for  absorption  by  rea.-^on  of  the  villi  and  the  valruhv 
cotniirciilrK.  Both  of  these  conditions  favor  absorption.  As  a 
matter  of  fa<t,  K5  per  cent,  of  the  ])roteid  has  been  foun<l  to  dis- 
appear. That  proteoxpn  and  peptotipx  are  alisorbed  directly  by  the 
blood  is  sb  >wn  in  ligating  the  thoracic  duct,  which  does  not  inter- 
fere with  ti  eir  disappearance.     Neverthele-ss  they  do  not  appear 


82  ABSORPTION. 

in  the  blood  as  such,  and  if  preseat,  act  as  poisonous  bodies  which 
cannot  be  used  by  the  tissues  and  are  immediately  excreted  by  the 
kidneys.  It  is  probable  that  the  epithelial  cells  convert  them  into 
serum  albumin.  Carbohydrates  which  are  changed  to  diffusible 
sugars,  dextrose,  and  levulose  are  also  absorbed  directly  into  the 
blood,  and  the  portal  vein  has  been  found  to  show  an  increased 
percentage  of  sugar  after  meals.  The  lymph  of  the  thoracic  duct 
shows  no  such  increase  unless  excessive  quantities  have  been  taken. 
Fats,  it  is  conceivable,  may  be  absorbed  in  an  emulsified  condition 
or  as  glycerine,  fatty  acids,  and  soaps.  Experimentally  it  has 
been  found  that  the  greater  part  of  the  fat  (60  per  cent.)  is  passed 
through  the  epithelial  cells  and  through  the  stroma  of  the  villi  to 
the  central  lacteal,  which  is  the  beginning  of  the  thoracic  duct. 
The  remainder,  however,  remains  unaccounted  for  and  may  be 
absorbed  by  the  blood  as  fatty  acid  and  glycerine.  There  is  very 
likely  a  synthesis  of  the.  latter  substances  in  the  body  of  the  epi- 
thelial cells  into  neutral  fat.  The  absorption  of  water  and  salts  by 
the  small  intestine  is  very  active,  but  there  is  also  a  secretion  of 
water  into  the  intestinal  lumen,  so  that  the  contents  remain  of  the 
same  fluid  consistency.  Water  and  salts  are  absorbed  directly 
by  the  blood  unless  excessive  quantities  are  taken,  when  a  portion 
passes  through  the  lymphatic  system,  accelerating  the  rate  of  flow 
of  the  chyle. 

ABSORPTION  FROM  THE  LARGE  INTESTINE. 

The  absorption  from  this  part  of  the  alimentary  canal  is  con- 
siderable, as  is  shown  by  the  changes  in  its  contents,  which,  enter- 
ing the  ileocsecal  valve  in  a  fluid  state,  are  converted  into  solid 
faeces.  Of  the  15  per  cent,  proteid  present,  some  is  absorbed  and 
some  is  destroyed  by  bacterial  action.  The  results  obtained  from 
nutrient  enemata  consisting  of  egg-albumen,  salt,  and  milkfat,  shoxo 
the  absorbing  capacity  of  the  large  intestine.  Animals  may  be 
kept  alive  by  this  method  of  nourishment,  although  no  enzymes 
are  present  to  digest  the  food. 

QUESTIONS  ON  CHAPTEE  V. 

What  conditions  are  present  in  the  alimentary  canal  that  favor  filtration 
and  osmosis  ? 

Give  proofs  that  epithelial  cells  are  active  during  absorption. 


METABOLISM.  83 

What  jfflths  may  iihsorbed  prcMlucts  take  in  tlicir  passage  into  the  blood? 
Distuss  the  ahsorptidn  tluit  take>  plaie  in  the  stomach. 
What  conditions  in  the  small  intestine  favor  absorption  ? 
Wliat  is  the  patli  taken  by  abs'>rl>ed  proteid? 
In  what  form  il<>  pmleids  apj  ear  in  tlic  blood? 
Where  are  they  clian}{e<l  ? 

What  is  the  fale  of  peptones  and  proteoses  injected  into  the  blood? 
Give  tlie  jiath  taken  by  absorbed  carbohydrates. 
How  are  fats  absorbed? 

Trace  the  path  of  fats  from  the  intestinal  lumen  into  the  blood. 
Discuss  the  absorption  of  water  in  the  small  intestine. 
What  paths  do  water  and  .sjilts  tiike  in  absorption  ? 
Discuss  the  ab.sori)tion  that  takes  place  from  the  large  intestine. 
What  change  in  the  consistency  of  the  couteats  of  large  and  small  intestine 
is  brought  about  by  absorption  ? 


CHAPTER   VI. 


METABOLISM. 


Having  traced  the  food  to  its  reception  in  the  blood,  it  will  he 
proper  to  consider  the  focts  that  are  known  concerning  its  further 
history.  The  food-stufls  are  rapidly  taken  to  all  portions  of  the 
body,  and  in  the  capillaries  are  transferred  through  their  walls  to 
the  Ivmph,  which  in  turn  brings  tht-ni  into  intimate  contact  with 
the  ti.-^«ue-cells.  Each  cell  extracts  from  the  lymph  the  substances 
that  it  needs  for  its  nourishment.  Then,  under  the  influence  of 
living  matter,  thev  undergo  a  .series  of  changes,  miaholie  and  knf<i- 
bnlic  in  nature,  which  converts  theni  finally  to  simple  stable  bodies 
possessing  little  energy.  This  is  shown  in  the  following  tables. 
During  twenty -four  hours  there  are  taken  into  the  body  : 

Food  (chemically  dry) 16  ounces. 

Water  (a.s  drink  and  as  combined  with  solid  food)    ...  80       " 

Oxypen  (absorbed  by  lunprs) ^6       '' 

ToUl 122  ounces. 

These  substances  are  converted  to  relatively  simple  bodies,  and 
leave  through  the  ordinary  excretory  channels — lung.s  skin,  kid- 
neys, and  intestines. 


84  METABOLISM. 

From  the  lungs  there  are  exhaled  every  twenty-four  hours — 

Of  carbonic  acid,  about 80  ounces, 

Of  water 10       "  40  ounces. 

Traces  of  organic  matter. 

From  the  skin — 

Water 23  ounces, 

Solid  and  gaseous  matter 1  ounce.      24       " 

From  the  kidneys — 

Water 50  ounces, 

Organic  matter 1|     " 

Minerals  and  salines ^  ounce.    52       " 

From  the  intestines — 

Water      •    •    • 4  ounces, 

Various  organic  and  mineral  substances  .    2       "  6       " 

Total 122"  ounces. 

The  income  and  expenditures  of  the  normal  adult  body  balance 
each  other. 

ENERGY  OF  FOOD. 

The  law  of  the  conservation  of  energy  teaches  that  the  sum-total 
of  energy  of  the  universe  is  constant,  and  that  it  can  be  neither 
created  nor  destroyed,  or,  in  other  terms,  increased  or  diminished. 
This  law  is  as  rigorously  true  for  the  body  as  for  any  physical 
system,  so  that  the  manifestations  of  living  bodies  must  be  the 
transformations  of  energy  brought  to  them  in  some  form  or  other. 
Of  all  the  sources  of  energy  to  the  body,  the  chemical  energy  of 
the  food  is  the  most  important.  It  is  in  a  potential  form,  and 
appears  in  kinetic  form  as  heat,  electricity,  and  mechanical  work. 
By  far  the  greatest  amount  appears  as  heat.  An  adult  man  in 
the  course  of  twenty-four  hours  will  liberate  about  2,400,000 
calories  of  heat — a  calorie  being  equal  to  the  amount  of  heat 
which  is  required  to  raise  one  cubic  centimetre  of  water  one 
degree  Centigrade. 

Since  the  energy  of  food-stuffs  is  set  free  by  their  physiological 
oxidation,  it  is  obvious  from  the  standpoint  of  the  doctrine  of  the 
conservation  of  energy  that  it  may  be  measured  by  burning  the 
food-stuffs  outside  of  the  body.  This  is  done  by  means  of  a  cal- 
orimeter, and  the  number  of  calories  of  heat  obtained  is  known  as 
the  combustion  equivalent  This,  in  round  numbers  for  proteids, 
has  been  found  to  be  4100  calories  ;  for  fats,  9300  calories  ;  and 
for  carbohydrates,  4100  calories.     These  food-stuffs,  as  far  as  their 


ENERGY  OF  Fool).  85 

poteutiiil  energy  is  concerned,  are  interchiin<;eiil)Ie,  so  tliiil  if  ciir- 
hohyd raters  are  to  take  the  place  of  tat.s,  they  must  he  furnished  in 
the  "ratio  of  i);U)():41()()  or  lus  2.2:1.  In  other  word.s,  it  Uikea 
more  than  twice  iw  much  carholiydrate  material  to  render  the 
s:imc  cncriry  as  any  given  amount  of  fat.  This  ratio  of  1  :  2.2  is 
known  as  the  iKodiindinir  tiiHinilciit. 

The  energy  produced  by  the  body  in  twenty-four  hours  nuiy  be 
measured  as  heat  in  two  ways  : 

1.  It  may  be  measured  directly  by  placing  the  animal  in  a 
calorimeter. 

2.  It  may  be  obtained  by  feeding  on  a  given  diet,  determining 
from  the  excreta  the  amount  of  food  destroyed,  and  multiplying  by 
the  proper  combustion  ecpiivalent.  These  methods  are  known  re- 
spectivelv  ;is  dirrrf  and  indirect  calorinictnj.  The  nutritional 
value  of  fooil-stutfs  cannot  be  estimated  from  their  contained 
energy  alone,  and  it  is  necessary  to  follow  the  changes  they  un- 
dergo in   their  metabolism  as  far  as  it  is  possiide. 

Proteid  is  taken  by  the  blood  to  the  tissues,  and  under  the  in- 
fluence of  living  matter  is  oxidized  to  carbon  dioxide,  water,  urea, 
.•<u//)hiife.%  and  pho^fphate.'^.  It  is  believed  that  a  part  of  the  pro- 
teid is  built  up  into  the  structure  of  living  matter  and  is  ilesig- 
nated  as  /(Vs/^e  ))r<)ti'id,  while  the  other  part  is  simply  destroyed 
and  is  called  circaldfiiKj  ])roteid.  These  terms  do  not  imply  that 
there  are  two  varieties  of  proteid.  but  refer  only  to  their  ultimate 
fiite.  Any  given  proteid  may  fulfil  either  function.  Since  living 
matter  is  es.sentially  nitrogenous  in  its  composition,  it  must  have 
some  source  of  nitrogen.  This  it  finds  in  proteid  food-stuffs,  which 
conse(|uently  are  absolutely  necessary  to  life.  No  animal  can  live 
for  any  length  of  time  on  fat  and  carbohydrate  food  alone,  but 
these  are,  nevertheles.s,  used  and  broken  down  in  the  body  to  fur- 
nish energy.  The  amount  of  proteid  destroyed  during  any  given 
time  is  indicatetl  by  the  amount  of  nitrogen  in  the  various  excreta, 
and  can  easily  be  determined  by  KjehhihrH  method. 

Place  5  c.c.  of  the  substance  to  be  tested  in  a  Kjeldahl  flask, 
and  aild  15  c.c.  of  sulphuric  acid  and  1  gramme  of  copper  sul- 
phate and  heat  until  foaming  cea.ses.  Then  add  10  grammes  of 
potassium  sulphate,  and  finally  a  little  pota.^^ium  permanganate, 
continuintr  the  boiling  until  the  liquid  is  light-green  in  color. 
Allow  to  cool,  and  transfer  the  contents  to  an  Erlenmeyer  flask, 
addiuLT   al)out    500  c.c.   of  water.     Adtl   also  a  little  talc  on   the 


86  METABOLISM. 

point  of  a  knife.  Insert  into  the  neck  of  the  flask  a  thistle  tube 
and  Reitmaier  bulb.  Connect  the  latter  with  a  condenser.  In 
the  receiving  flask  place  50  c.c.  of  decinormal  oxalic  acid  solution, 
which  will  unite  with  the  ammonia  that  is  to  be  distilled  off". 
When  everything  is  ready,  put  into  the  flask  strong  sodium 
hydrate  until  the  contents  are  alkaline  ;  then  heat  and  distil  over 
about  200  c.c.  of  the  liquid.  Add  to  the  distillate  a  few  drops  of  an 
alcoholic  solution  of  rosolic  acid,  and  titrate  with  decinormal 
sodium  hydrate  solution  to  a  deep  pink  color.  When  the  nitro- 
gen of  the  excreta  equals  the  amount  ingested  as  food,  an  animal 
is  said  to  be  iu  nitrogenous  equilibrium.  Likewise  carbon  equilib- 
rium is  a  condition  in  which  the  total  carbon  of  the  excreta  (COj, 
urea,  etc.)  is  equal  to  that  taken  in  the  food.  When,  from  the 
total  carbon,  there  is  subtracted  the  amount  that  belonged  to  pro- 
teids  broken  down,  the  remainder  is  an  indication  of  the  carbo- 
hydrates and  fats  that  were  used.  An  animal  may  be  in  both 
nitrogen  and  carbon  equilibrium  at  the  same  time,  or  may  be  in 
either  alone.  If  an  animal  is  giving  off"  more  nitrogen  in  the 
excreta  than  it  receives  in  the  food,  it  must  be  losing  the  proteid 
of  its  body  and  so  losing  in  weight,  but  if  the  nitrogen  given  ofi" 
is  less  than  that  of  the  food,  the  animal  must  be  storing  up  proteid 
and  gaining  in  weight. 

It  would  seem  that  if  proteid  fulfils  two  functions,  enough  might 
be  given  to  an  animal  to  cover  the  tissue  waste  and  the  balance 
of  the  food  might  be  given  as  energy  producing  fats  and  carbo- 
hydrates, and  still  maintain  nitrogen  equilibrium.  This  is  not 
the  case,  however.  It  requires  more  proteid  than  is  theoretically 
necessary.  Part  of  it  is  always  used  as  circulating  proteid  which 
carbohydrates  cannot  replace.  The  fact  that  proteids  are  always 
taken  in  excess  of  what  is  necessary  to  just  cover  tissue  waste  has 
led  to  the  designation  of  the  excess  as  a  luxus  consumption.  This 
is  an  inappropriate  term,  since  animals  which  only  receive  enough 
nitrogen  to  cover  tissue  waste  show  nutritional  disturbances  for  the 
reasons  already  given. 

Albuminoids  resemble  proteids  in  percentage  composition,  but 
cannot  be  used  to  maintain  nitrogen  equilibrium  nor  for  the  forma- 
tion of  new  tissue.  They  serve,  however,  as  a  source  of  energy, 
and  can  take  the  place  of  circulating  proteids.  The  value  of 
albuminoids  as  a  food  is  limited  because  of  the  aversion  that  its 
continued  use  produces. 


EXhlUiV   OF  FOOD.  87 

Carbohydrates  aro  ()xi<li/,('(l  imd  funiihli  enertry.  They  may  be 
c'oiivirud  inti)  Iht,  and  stored  as  reserve  luati-rial.  ( )t'  the  eiid- 
prodiK'ts,  CO.,  and  II,(),  the  hitter  obtains  its  oxy^^-n  from 
the  earbohydratt  molecule,  so  that  only  enough  a<ldilional  oxy- 
gen is  required  to  oxidize  the  carbon.     The  respiratory  quotient, 

CO,    /carbonic  aci(l\ 

^7z^  ,  therefore  approaches  uuity  as  the  carbohv- 

O,     \      oxygen      f  '^  ^ 

drates  in  the  meal  are  increased.  These  food-stuHs,  like  proteids, 
are  first  split  before  undergoing  oxidation.  Dextrose  in  its  pas- 
sage through  the  liver  is  converted  to  animal  starch  or  glycogen. 
It  may  be  detected  by  the  port-wine-red  color  which  it  gives  with 
iodine.  Microscopically,  it  can  be  seen  to  disajipear  during  fast- 
ing and  to  increase  after  meals.  The  amount  formed  depends 
upon  the  character  and  quantity  of  the  food,  exercise,  temperature, 
etc.  It  forms  from  1.5  to  4  per  cent,  of  the  weight  of  the  liver, 
and  may  be  increa.^^ed  to  10  per  cent,  by  a  rich  carbohydrate  diet. 
Cilycogen  may  also  be  produced  from  purely  proteid  food,  l)ut  not 
from  fats.  It  seems  that  the  proteid  molecule  is  split  into  a  nitro- 
genous and  a  nou-uitrogeuous  portion,  and  that  the  latter  forms 
glycogen.  Glycogen  performs  a  useful  function  as  a  temporary 
re.servf  store,  for,  if  the  dextrose  formed  during  digestion  be  pas.'Jed 
directly  into  the  general  circulation,  the  jiercentage  of  sugar  would 
be  increased  at  loo  raind  a  rate  and  would  then  be  excreted  l)y 
the  kidneys.  It  is,  therefore,  stored  up  liy  the  liver  as  glycogen, 
and  from  time  to  time,  as  the  demand  arises,  is  reconverted  to  dex- 
trose and  secreted  into  the  blood,  so  that  the  sugar  in  the  latter 
remains  nearly  constant  (0.1  to  0.2  per  cent.).  It  is  found  that 
after  the  liver  is  removed  from  the  body  its  supply  of  glycogen 
quickly  disappears,  and  dextrose  is  found  instead.  In  this  con- 
nection it  is  interesting  to  know  that  extracts  of  the  liver  yield  an 
amylolytic  enzyme  which  converts  glycogen  into  dextrose.  The 
dextrose  that  the  liver  gives  to  the  blood  is  taken  to  the  tissues, 
and  in  time  is  oxidized.  It  may,  however,  again  be  stored  in 
the  muscles  as  glycogen.  These  contain,  when -at  rest,  0.5  to 
0.9  per  cent,  and  in  the  entire  muscular  system  there  is  as 
much  as  is  present  in  the  liver.  When  a  muscle  is  active,  it.^ 
store  of  glycogen  quickly  disappears.  It  has  been  shown  that 
an  isolated  muscle  when  irrigated  with  blood  containing  dex- 
trose can  form  glycogen;    also  that  an   active  muscle  will   take 


88  METABOLISM. 

up  more  sugar  from  au  artificial  supply  of  blood  than  a  resting 
muscle. 

Fats  which  reach  the  circulation  as  neutral  fats  are  taken  to  the 
tissues,  and  in  time  are  converted  to  CO^  and  H^O.  They  contain 
more  available  energy,  weight  for  weight,  than  carbohydrates. 
The  body  fat,  particularly  that  of  the  panniculus  adiposus,  is  a 
reserve  supply,  and  is  drawn  upon  whenever  the  need  arises.  The 
origin  of  fat  was  at  first  supposed  to  be  simply  that  which  was 
taken  in  as  food,  but  the  history  of  fat  as  seen  microscopically 
showed  that  it  was  not  simply  deposited,  and  it  was  soon  demon- 
strated that  in  cows  and  pigs  an  amount  of  fat  might  be  formed 
out  of  all  proportion  to  the  amount  ingested.  In  addition  to  this 
it  was  found  that  the  fat  of  an  animal  differed  in  kind  from  that 
which  was  taken  in  as  food.  It  has  been  definitely  decided  that 
only  under  special  conditions,  as  when  an  animal  is  richly  supplied 
with  fats,  are  the  latter  stored  directly.  Usually  the  fat  of  the 
food  is  completely  oxidized,  and  that  which  is  stored  is  derived 
from  carbohydrates  and  proteids.  The  latter  is  an  important 
source ;  the  theoretical  maximum  that  it  can  yield  is  about  51.5 
per  cent.  It  has  been  shown  that  in  a  young  pig  the  amount  of 
fat  laid  on  in  a  given  time  was  greater  than  that  obtained  from  the 
food  directly,  plus  the  theoretical  maximum  obtainable  from  pro- 
teids, so  that  it  must  have  come  from  the  ingested  carbohydrate 
food.  It  is  of  interest  that  the  Banting  diet  for  reducing  obesity  is 
characterized  by  the  absence  of  carbohydrates  and  the  excess  of  pro- 
teids. 

Water  is  lost  through  the  skin,  lungs,  kidneys,  and  fseces.  It  is 
replaced  in  the  food  as  such,  and  also  as  part  of  the  structure  of 
food-stufis.  It  is  not  a  source  of  energy,  but  serves  as  a  menstruum 
in  which  metabolism  takes  place.  Deprivation  by  changing  the 
composition  of  the  tissues  leads  to  death. 

Salts. — Sodium  chloride  is  the  only  salt  usually  taken  deliber- 
ately with  the  rest  of  the  foods.  Salts  are  not  a  source  of  energy, 
and  most  of  them  are  eliminated  as  they  are  taken  in.  Sodium 
chloride  in  the  formation  of  the  acid  of  the  gastric  juice  is  an 
exception.  Some  of  the  sulphates  and  phosphates  are  formed  in 
the  body.  The  general  function  of  salts  is  to  preserve  imbibition 
relations.  Diets  which  are  entirely  lacking  in  saline  constituents 
fail  to  preserve  life  at  all,  even  when  they  are  present  in  proper 
amount  and  kind  separately — so  that  they  seem  to  be  ordinarily  in 


DETERMISATIOX   <>F  MI'/l'MK H.ISM.  8!) 

organic  combination  witii  footl-stiilis.  (  uniirora  do  not  crave  salts 
UH  hcrbivora  do.  This  i.s  explained  hy  ]iunge  as  l)eing  the  re.sult 
of  the  fact  that  phmtii  contain  an  excess  of  jK)ta8sinni  salts,  which 
react  with  sodium  chloride  to  form  potassium  chloride  and  a  cor- 
nspondini;  sodium  salt,  which  are  excreted  ])y  the  kidneys  when 
they  reach  above  a  normal  limit.  The  following  uses  of  cnlciniii 
xdlt.-f  have   been  given  : 

1.  riiey  are  necessary  to  the  development  of  the  bones,  as  a 
dill  poor  in  calcium  salts  brings  about  a  condition  sinnlar  to 
rickets  in  children. 

2.  They  are  necessary  to  the  coagulation  of  blood,  lymph,  and 
milk. 

o.  They  are  necessary  to  the  rhythmic  activity  of  the  heart  and 
to  the  normal  activity  of  all  protoi)lasm. 

The  calcium  acquired  and  lost  by  the  body  normally  is  very 
small  in  amount,  and  is  excreted  mainly  through  the  intestinal 
walls.  The  main  portion  of  the  calcium  of  the  fieces,  however, 
is  that  ingested  with  the  food,  and  simply  passes  through  the  canal. 
It  is  probable  that  the  calcium,  in  order  to  be  absorbed,  must  be 
in  organic  combination.  The  salts  of  iron  are  of  importance  in 
their  relation  to  haemoglobin,  which,  being  continually  lost,  must 
l)e  replaced.  ^lost  of  the  iron  of  the  food,  including  that  of  the 
luemoglobin  of  meats,  is  passed  out  imchanged  in  the  fieces,  and 
to  this  is  added  a  slight  excretion  of  iron  from  the  intestinal  walls. 
The  iron  absorbed  by  the  system  is  probably  in  the  form  of  organic 
compounds. 

DETERMINATION  OF  METABOLISM. 

In  determining  body-metabolism  the  nitrogen  of  the  excreta  is 
multiplied  1)y  6.2")  to  give  the  amount  of  ]iroteid  destroyed.  The 
value  fi.2o  is  obtained  from  the  proporti(m — proteid  molecule  : 
nitrogen  contained  :  :  100  :  IG.  It  has  been  ascertaine<l  by  numerous 
analyses  that  on  an  average  the  nitrogen  forms  almut  16  per  cent, 
of  the  proteid  molecule.  The  metabolism  of  the  body  varies 
greatly  with  its  condition.  It  has  long  been  known  that  muscular 
work  increases  metabolism,  and  since  the  latter  involves  living 
matter,  which  is  essentially  nitrogenous,  it  was  thought  that  there 
must  be  a  sinndtaneous  increase  in  the  out])Ut  of  urea.  But 
numerous  experiments  have  shown  that  this  is  not  usually  the  case. 


90  METABOLISM. 

During  severe  labor,  however,  upon  a  diet  insufficient  in  carbohy- 
drates and  fats,  the  proteids  of  the  body  are  drawn  upon  to  furnish 
energy,  and  there  is  then  an  increase  in  the  excretion  of  urea. 
The  carbon  dioxide  is  markedly  increased  by  muscular  activity,  in 
intact  organisms  as  well  as  in  isolated  muscles.  Since  nitrogenous 
components  are  not  used  up,  the  energy  must  come  from  non-nitro- 
genous food-stuffs,  or  from  non-nitrogenous  portions  of  the  biogen. 
During  sleep  the  excretion  of  urea  is  not  diminished,  but  that  of 
carbon  dioxide  is  distinctly.  In  general  the  consumption  of  .non- 
nitrogenous  material  increases  with  the  fall  of  the  outside  temper- 
ature, providing  that  of  the  body  remains  constant,  therefore  while 
the  excretion  of  carbon  dioxide  increases,  that  of  urea  is  un- 
changed. In  pathological  cases  with  an  excessively  high  or  low 
body-temperature,  the  metabolism  of  both  proteid  and  non-proteid 
is  changed.  High  temperatures  increase,  and  low  temperatures 
decrease,  the  output  of  waste  matters.  In  starvation  an  animal  uses 
its  reserve  material,  and  then  lives  on  its  own  tissues.  During  the 
first  day  or  two  of  starvation  the  quantity  of  proteid  destroyed  is 
greater  than  on  subsequent  days,  when  the  circulating  proteids 
have  been  destroyed  and  only  tissue-proteids  and  non-proteids  re- 
main. After  the  latter  substances  have  disappeared,  shortly  before 
death,  there  is  an  increased  excretion  of  urea,  for  the  animal  is 
then  entirely  dependent  upon  tissue  proteids  alone.  In  starvation 
the  various  tissues  and  organs  are  differently  affected.  Muscles 
suffer  most  absolutely,  and  fats  most  relatively,  while  organs  in 
continuous  activity,  like  the  heart  and  central  nervous  system,  lose 
practically  nothing. 

QUESTIONS  ON  CHAPTER  VI. 

How  do  the  food-stuffs  reacli  tlie  tissue-cells? 

Define  "conservation  of  energy." 

Does  the  law  of  the  conservation  of  energy  hold  true  for  the  body? 

What  is  the  source  of  energy  of  the  body? 

Into  what  forms  of  energy  does  the  body  convert  the  energy  of  the  foods? 

How  much  heat  is  given  off  by  the  body  per  day  ? 

Define  a  calorie. 

Discuss  the  "combustion  equivalent"  of  foods. 

How  is  the  combustion  equivalent  obtained? 

Into  what  simple  bodies  are  proteids  converted  by  the  body? 

Give  the  combustion  equivalent  of  proteids,  carbohydrates,  and  fats. 

Discuss  the  isodynamic  equivalent  of  fats  to  carbohydrates. 

Discuss  circulating  and  tissue  proteids. 

Why  is  proteid  necessary  to  the  animal  economy? 


BLOOD   AM)    J.YMPU.  91 

Give  the  nu'th(Kl  of  tlie  (IcUiniiiiiiition  of  total  nitrogen. 

What  is  mt'aiit  liy  iiilrunt'ii  and  carlxm  c(|iiilii)i'iniu Y 

Iltiw  arc  the  dcstnivcd  carholiydratos  deti-rininuilY 

Discii.ss   "  luxiis  ((iii^iiniiitidh."  • 

Wliat  is  the  nutritive  value  of  alhuniinuidsV 

Into  what  simple  suijstances  are  carbdhydratcs  convorted? 

W'hiit  happens  to  the  respiratory  ijiiotient  as  the  result  of  a.  carbohydrate 
diet  ? 

Are  the  various  food-stulls  directly  oxidized? 

Give  the  liistory  of  glycogen. 

Give  tile  iiuantity  of  glye(j><en  in  liver  and  muscle. 

What  is  the  percentage  of  dextrose  iu  the  blood  V 

Into  what  sim|>le  bodies  are  fats  changed  ? 

What  are  the  function  and  the  origin  of  the  l)ody-fat? 

Give  proofs  as  to  the  origin  of  fat. 

What  values  have  water  and  .salts  to  the  animal? 

What  .salt  especially  undergoes  a  change  in  the  bodj' ? 

Why  do  herbivora  crave  salt.s? 

What  are  the  sources  of  the  salts  of  the  body? 

What  are  the  uses  of  calcium  salts? 

How  is  the  amount  of  jiroteid  broken  down  by  an  auinial  determined  from 
the  nitrogen  of  the  excreta? 

How  is  metabolism  varied  under  difl'erent  conditions? 

Is  the  excretion  of  urea  increased  by  muscular  work?  Is  the  excretion  of 
CO2  increased  ? 

Give  changes  in  nietabolism  during  starvation. 

How  are  the  difterent  organs  atTected  by  starvation  ? 


CHAPTER    VII 

BLOOD  AND  LYMPH. 
BLOOD. 


The  blood,  a  chemically  complex  fluid  contained  within  the 
vessels  of  the  body,  hjis  been  recognized  from  the  earliest  times  as 
indispensable  to  tlie  life  of  man.  An  excefo^ive  hemorrharje  pros- 
trates, enfeebles,  and  may  cause  death.  This  becomes  evident 
when  it  is  known  tliat  the  blood  carries  to  the  tissues  material  for 
their  c/roirfh  and  rrjjalr,  and  removes  from  them  inaffcr.-^  that  have 
become  rjf'cfr.  It  equalizes  the  tenijicratiirr  of  the  body,  and 
mtiintains  uniform  Imhihifioii  rrlafions  lietween  the  ('ell.-<.  It  is  an 
intenial  meflium.  that  liears  the  same  relations  to  the  ihxnm  that 
the  oidrr  world  does  to  the  entire  body.  It  forms  in  total  nearly 
one-thirteenth  of  the  bodi/-v<eight,  so  that  a  man  of  170  pounds  will 
possess  over  li  pomuh  of  blood,  or  nearly  G  (juarf.<     In  given 


92  BLOOD  AND  LYMPH. 

individuals  it  does  not  vary  through  any  wide  limits.  Variations 
that  are  brought  about  by  loss  of  water  as  by  perspiration  or  by  a 
gain  of  water,  as  through  the  ingestion  of  excessive  quantities  of 
water,  are  compensated  for  by  a  passage  of  fluid  from  or  to  the 
tissues.  In  starvation  the  quantity  and  the  quality  of  the  blood 
are  maintained  at  the  expense  of  the  other  tissues.  An  estimation 
of  the  amount  of  blood  of  an  animal  is  made  by  measuring  di- 
rectly as  much  as  will  escape  from  the  vessels.  The  latter  are 
then  washed  out  with  normal  saline  solution,  and  the  tint  of  the 
washing  is  matched  by  diluting  a  given  quantity  of  normal  blood. 
This  process  is  repeated  after  carefully  mincing  the  entire  body. 
The  blood  in  the  washings  may  be  calculated  by  knowing  the  dilu- 
tion of  normal  blood  required  to  match  it.  This,  added  to  the 
amount  measured  directly,  gives  the  total  quantity.  It  is  distri- 
buted in  the  body  as  follows  : 

One-fourth  in  the  heart,  lungs,  large  arteries,  and  veins. 

One-fourth  in  the  liver. 

One-fourth  in  the  skeletal  muscles. 

One-fourth  in  the  remainder  of  the  body. 

The  blood  consists  of  a  fluid  plasma  (liquor  sanguinis),  in  which 
are  suspended  cells  called  hlood-corpuscles.  It  may  he  regarded  as 
a  tissue  of  which  the  intercellular  matrix  is  a  fluid.  Freshly 
drawn,  it  is  of  a  bright  scarlet  color  when  taken  from  the  arteries 
or  pulmonary  veins,  but  crimson  when  taken  from  the  systemic 
veins.  This  is  the  result  of  different  oxidation  stages  of  the  pig- 
ment hcemoglobin,  which  is  contained  in  the  red  corpuscles.  The 
blood  is  opaque,  caused  by  the  fact  that  its  solid  elements  opjoose 
the  transmission  of  light  by  reflecting  it  back  from  their  surfaces. 
In  various  ways,  as  by  the  addition  of  ether,  bile,  excess  of  water, 
by  freezing  and  thawing,  etc.,  the  coloring-matter  may  be  driven 
from  the  corpuscles  into  solution  in  the  plasma,  leaving  a  delicate, 
colorless  cell-body,  through  which  the  light  passes  readily.  The 
blood  is  then  transparent,  and  is  known  as  laky  blood.  The  spe- 
cific gravity  varies  from  104-1  to  1067,  according  to  age,  sex,  state 
of  health,  meals,  exercise,  and  sleep.  Its  slightly  alkaline  reaction 
is  due  to  the  phosphates  and  carbonates  of  the  alkaline  metals. 
Estimated  as  sodium  carbonate,  it  is  equal  to  0.35  per  cent. 
Ordinary  litmus-paper  cannot  be  used  in  testing  the  reaction  of 
the  blood,  owing  to  the  fact  that  it  stains.  Soaking  in  saturated 
salt  solution  covers  the  paper  with  a  layer  of  salt  that  holds  the 


BLOOD.  93 

corpuscles,  and  wliidi  may  tlicii  readily  l)i'  washed  off.  It  never 
becomes  acid.  IJlood  has  a  sahy  l(i.'<lc,  and  a  peculiar,  character- 
istic odor.  The  tciiijicratKre  is  about  WH.y°  F.,  but  probably  is 
hiiihcr  in  the  internal  parts  of  the  body. 

Corpuscles. 

The  corpuscles  of  the  blood  are  of  at  least  three  kinds — red 
corj)usc/c.-i  {eri/fltrocytes),  white  cor j) uncles  (leiicocyleH),  and  blood- 
plates  (microcijtes).  The  red  cells  may  be  put  at  5,000,000  per 
c.nira.  for  males,  and  at  4,500,000  for  females,  as  an  average 
number.  Their  number  varies  with  the  constitution,  nutrition, 
manner  of  living,  and  age  of  the  individual.  They  are  most 
numerous  in  the  embryo  and  young.  In  the  adult  their  nundier 
is  at  a  minimion  after  meals;  it  is  increa.nd  during  menstruation, 
and  decreased  during  i)regnancy.  Chaiif/e  of  olfitiide  has  been 
found  to  exert  a  most  remarkable  influence.  A  mountain  life  has 
been  found  to  raise  the  average  number  to  8,000,000,  and  to  in- 
crease the  contained  hivmoglobin  as  well.  A  return  to  a  lower 
level  brings  back  the  blood  to  its  normal  state.  A  diminished 
pressure  of  o.vi/r/en  in  the  blood,  whether  jjroduced  by  high  alti- 
tudes or  by  the  actual  loss  of  blood,  stimulates  to  greater  aclirity 
the  //.s.sv<f.s  that  form  new  corpuscles. 

When  viewed  under  the  microscope  ivdividiialli/,  each  corjniscle 
is  of  a  faint  yclloiri.^h  color.  Each  consists  of  an  extensil)le,  pro- 
toplasmic material  known  as  stroma,  which  gives  shape  to  the  cor- 
puscle and  holds  the  haemoglobin.  The  latter,  forming  90  per 
cent,  of  the  solid  matter  of  the  corpuscle,  is  held  in  some  weak 
chemical  cond)ination  with  the  stroma,  since  its  behavior  within 
the  corjMiscle  differs  from  that  when  separate. 

Haemoglobin  is  a  meml)er  of  the  group  of  cond)ined  proteids. 
It  may  be  separated  in  various  ways  into  a  proteid  body,  (j/obin 
(9()  per  cent.),  and  a  sim])ler  pigment,  hamatin  (4  per  cent.), 
together  with  other  bodies  whose  nature  is  unknown.  If  the  de- 
composition takes  place  in  the  absence  of  oxygen,  hamochromofjen 
is  formed  instead  of  h.Tmatin.  It  is  the  hiTmochromogen  that 
gives  to  hiemoglobin  its  jieculiar  power  of  taking  up  o.ry()eii  into 
loose  chemical  combination.  There  are  J4  f/rammes  of  hamot/lobin 
to  every  100  </r<imme.^  (f  blood,  no  that  a  man  vcif/hitK/  OS  //Aw  has 
750  grammes  of  hamogbdiin   di.^tributcd  amoiuj  J.'J  trillions  of  cor- 


94  BLOOD  AND  LYMPH. 

puseles,  giving  a  superficial  area  of  about  S200  square  metres.. 
This  is  important  from  a  respiratory  point  of  view,  as  the  entire 
surface  is  practically  exposed  to  the  absorption  of  oxygen.  Haemo- 
globin will  take  1.59  c.c.  of  oxygen  to  each  gramme  weight,  and 
form  in  so  doing  a  compound  known  as  ozyhcemoglobin.  The 
latter,  if  placed  in  an  atmosphere  which  is  deficient  in  oxygen,  will, 
be  converted  by  the  loss  of  oxygen  to  reduced  licemoglobin. 
Haemoglobin  has  the  power  of  combining  with  a  number  of  other 
gases.  With  carbon  monoxide  it  unites  in  the  proportions  of  one 
volume  to  one  of  haemoglobin,  forming  carbomonoxide-hcemoglobin, 
which  is  more  stable  than  oxyhaemoglobin,  so  that  it  is  not  easily 
converted  into  ordinary  haemoglobin.  This  explains  the  fatal 
effects  produced  by  breathing  illuminating  gas,  which  contains  car- 
bon monoxide  as  a  constituent.  The  oxygen  of  the  air  is  prevented 
from  uniting  with  haemoglobin  and  thus  produces  asphyxia.  Nitric- 
oxide  (NO)  produces  a  still  more  stable  combination.  Carbon 
dioxide  (CO2),  however,  which  in  its  reaction  with  haemoglobin 
produces  carbohcemoglobin,  unites  with  a  different  part  of  the 
haemoglobin  molecule  since  it  does  not  interfere  with  the  absorp- 
tion of  oxygen.  Thus  is  explained  the  action  of  this  gas  as  an 
ancesthetic.  It  has  been  suggested  that  the  carbon  dioxide  unites, 
with  the  proteid  portion,  and  it  makes  possible  the  transportation 
of  carbon  dioxide  by  haemoglobin  from  the  tissues,  where  it  is 
given  off  as  a  waste-product  to  the  lungs,  where  it  is  removed 
from  the  body.  The  most  characteristic  feature  of  haemoglobin 
is  the  presence  of  iro7i,  which  amounts  to  about  0.47  per  cent.,  so 
that  an  estimation  of  the  iron  of  the  blood  would  be  a  method  of 
determining  the  amount  of  haemoglobin.  This  element  remains  a 
part  of  haematin  when  haemoglobin  is  decomposed,  and  upon  it 
depends  the  affinity  of  haemoglobin  for  oxygen.  One  atom  of  iron 
will  take  up  one  molecule  of  oxygen.  Both  oxy-  and  reduced 
hoemoglobin  are  crystallizable.  A  good  method  is  to  shake  the 
blood  in  a  test-tube  until  it  becomes  laky,  and  then  place  it  on 
ice  until  the  crystals  form.  They  have  different  forms  in  different 
animals — for  example,  those  of  man  and  most  mammalia  are 
rhombic  prisms ;  of  the  squirrel,  rhombic  plates  ;  and  those  of  the 
guinea-pig,  tetrahedra.  These  crystals  are  soluble  in  water,  but 
do  not  dialize.  Haematin  unites  with  hydrochloric  acid  (HCl)  to 
form  hcemin,  the  crystals  of  which  are  of  the  greatest  importance 
in  the  identification  of  blood-stains.     Scrapings  from  the  stain  are 


BLOOD. 


95 


pl:i(^0(l  on  a  jjlass  slide,  and  a  drop  of  a  1  per  cent,  solution  of 

sodium  fhloride  (iSaCl)  is  added.  Heat  over  a  <,'entle  flame, 
avoiding  ehuilitiun  until  the  water  has  nearly  evaporated.  Then 
([uicklv  add  one  or  two  drops  of  "xiacial  acetie  aeiil,  cover  with  a 
(•ovi'r-ii:la>s,  and  airain  warm  until  tlu'  acid  ha.s  nearly  disappearetl. 
When  cool,  microscopic,  characteristic,  hrown  (■rt/--<t(i/s  are  depos- 
ited.    Together  with  the  spedroscupic  ted  they  indicate  positively 


Red.    Orange. Y.llow.  (i 


mB 


c 


11 


^  aJ3  C       J> 


is^m itiL 


Fio.  6. 

Blue. 


'■"T^"T""I = 


5 


iDdlgo. 


OxyhEemc)globin  and 
NO;.-lia;moglobin. 


CO-hsemoglobiu. 


Reduced  ha-moglobin. 


Hffimatin  in  acid  solu- 
tion. 


Hfeniatin  in  alkaline 
solution. 


Reduced  haematin. 


Polar  spectrum  with 
Fraunhofer's  lines. 


JS      i4 


the  presence  of  blood.  The  presence  of  cells  of  certain  size  and 
non-nucleate<l  ones  will  exclude  the  blood  of  certain  animals,  but 
it  is  not  sufficient  evidence  of  human  blood.  Mammals  have  iioii- 
niichafcd  cclh. 

Scjlutions  of  iKcmoLdobin  and  coin])ounds  derived  from  it  give 
characteri.^^tic  absorption  bands.  The  spectrum  of  a  dilute  solu- 
tion of  oxyluemogloliin  shows  two  dark  band.s,  both  between  the 
lines   D  and  E.     That   nearer  the  red  end  of  the  spectrum,  or 


96  BLOOD  AND  LYMPH. 

alpha  hand  as  it  is  called,  is  darker,  narrower,  and  more  distinct 
than  the  other  or  beta  hand.  The  distinctness  and  width  of  the 
band  vary  with  the  density  of  the  solution.  With  very  dilute 
solutions  only  a  faint  alpha  band  is  present ;  with  stronger  solu- 
tions the  bands  grow  wider,  fuse,  and  finally  shut  off  all  light. 
The  orange  is  the  last  to  disappear.  If  a  solution  of  oxyhsemo- 
globin  is  converted  to  reduced  haemoglobin  by  the  addition  of 
Stakes'  reagent  (an  ammoniacal  solution  of  a  ferrous  salt),  only 
one  absorption  band  is  seen,  called  the  gamma  hand,  which  lies 
between  the  lines  D  and  E.  The  position  of  these  bands  be- 
comes readily  apparent  by  referring  to  the  accompanying  figure 
(Fig.  6). 

The  length  of  life  of  a  red  hlood-corpuscle  is  not  known.  Since 
hgemoglobin  forms  the  mother  substance  of  the  bile-pigments  which 
are  continually  being  passed  from  the  body,  and  also  since  the  cor- 
puscles are  non-nucleated,  it  is  believed  that  they  are  continually 
undergoing  disintegration  in  the  blood-vessels.  They  are  replen- 
ished by  special  corpuscle-forming  or  haematopoietic  tissues,  the 
process  of  production  being  known  as  ha;matopoiesis.  The  red 
marrow  of  the  ho7ies  is  the  most  marked  example  of  such  tissue. 
Here  groups  of  nucleated  colorless  cells  known  as  erythroblasts 
undergo  karyokinesis,  and  the  daughter-cells,  after  forming  haemo- 
globin in  their  cytoplasm,  are  nucleated  corpuscles  which  in  time 
extrude  their  nuclei  and  are  forced  by  the  growing  tissue  into  the 
blood-stream.  In  the  embryo  the  liver  and  the  spleen  also  pro- 
duce new  red  corpuscles. 

White  Blood-cells. — These  are  variously  classified.  Ehrlich 
makes  three  divisions — oxyphiles  or  eosinophiles,  whose  gramdes 
are  stained  with  acid  stains;  hasophiles,  xvhich  stain  only  uithhasic 
stains;  and  neutrophiles,  ivhich  stain  only  with  neutral  dyes. 

A  simpler  classification  may  be  made  : 

1.  Lymphocytes,  small,  having  a  round  vesicular  nucleus  and 
scanty  cytoplasm. 

2.  Mononuclear  leucocytes,  large,  having  a  vesicular  nucleus  and 
abundant  cytoplasm. 

3.  Polynuclear  leucocytes,  large,  ivith  nucleus  divided  into  lobes 
or  into  distinct  parts. 

4-.  Eosinophile  cells,  like  the  last,  but  with  cytoplasm  filled  with 
coarse  granules. 

It  is  possible  that  the  members  of  the  last  classification  may  be 


ULoolK  97 

projrressive  stages  in  tlu'  irrowtli  of  a  t-iiiirle  kind  of  cell,  the  lyni- 
pliocvte  foiMniuL'  the  yi)un<,a'St.  while  t lie  polyiiuclear  <'ell  forms  (lie 
idilest  istai^e.  Leiieoc-vtes  show  aiiKehoid  iiioveineiils  which  enables 
them  to  move  from  place  to  place  (therefore  calle<l  irandcriiuj 
cells),  and  even  to  j)ierce  the  walls  oi' the  Mood-vessels  an<i  j^-et  into 
the  lymph-spaces.  This  process  is  known  as  didpt'deniK.  Their 
iuind)er  is  put  at  about  7500  per  o.mni.  A  marked  increase  in 
number  (lenconjioi^ix)  is  seen  in  ieukiomia. 

Function  of  Leucocytes. — A  numl)er  of  suggestions  have  been 
made  as  to  this  : 

1.  They  jirotect  the  body  from  disrme  by  ingesting  patliogeuic 
/vr/'7fr/rt  (  phagocytosis).  ISucli  cells  are  known  as  pltayocyk'^  ;  or 
ihev  may  fjiiard  the  body  by  the  formation  oi  protective  prote'ids 
which  destroy  disease-germs. 

2.  They  aid  in  the  abmrption  of  fats  and  peptones. 
'A.  They  take  part  in  the  coagulation  of  the  blood. 

4.  They  help  to  maintain  the  normal  composition  of  the  blood  in 
regard  to  its  proteids,  since  the  latter  are  not  all  formed  directly 
from  absorbed  food.  They  do  this  by  undergoing  tlisintegration 
in  the  blood  and  by  active  metabolic  changes  which  are  indicated 
by  their  cytoplasm  in  the  formation  of  zymogen  granules.  Leuco- 
cytes multiply  by  karyokinetic  division,  and  are  also  newly  formed 
in  the  lymph-glands  and  lyiujihoid  tissue. 

The  blood-plates  are  small  circular  or  oval  bodies  of  homoge- 
neous structure  and  of  variable  size.  Their  number  is  about 
'2.30,000  per  c.mm.  They  are  not  independent  cells,  and  therefore 
soon  disintegrate.  Cf^mposed  of  the  same  substance  as  the  nuclei 
of  leucocytes,  they  are  often  regarded  as  nothing  more.  They  take 
part  in  the  coagulation  of  the  l)lood. 

Plasma. 

The  plasma,  which  is  an  alkaline,  viscid,  straiv-colored  fluid  of  a. 
apedjic  gravitij  of  1030,  may  be  obtained  in  a  number  of  ways: 
The  blood  may  be  cooled,  in  which  ca.«!e  coafj/itlafion  takes  place 
sloivh/  and  the  corpuscles  have  time  graduallv  to  sink  to  the  bot- 
tom of  the  vessel.  The  corpuscles  having  a  specific  gravity  of 
108Harethe  heaviest  com])onents  ol"  the  blood.  When  blood  is 
received  directly  into  neutral  salt  solutions,  as  sodium  or  magne- 
sium sulphate,  it  will  not  clot.     The  corpuscles  may  then  be  allowed 

7— Phys. 


98  BLOOD  AND  LYMPH. 

to  sink,  or  they  may  be  centrifugalized  off.  The  method  of  action 
of  the  salt  is  not  known. 

Peptones  and  alhumoses,  when  injected  into  an  animal,  will  pre- 
vent the  clotting  of  its  blood  for  a  long  time.  But  peptone  added 
to  blood  already  shed  has  no  such  effect.  The  action  of  the  peptone 
in  the  body  is  explained  in  that  it  causes  a  rapid  destruction  of 
leucocytes.  This  sets  free  two  substances — a  uucleoproteid  and 
liiston.  The  first  takes  part  in  the  formation  of  fibrin  f&rment, 
which  is  destroyed  by  the  liver,  while  the  second,  which  is  known 
to  be  antagonistic  to  the  coagulation  of  the  blood,  is  left  in  the 
blood-vessels.  The  addition  of  oxalate  solutions  by  precipitating 
the  soluble  calcium  salts  will  prevent  coagulation. 

Plasma  consists  of  water,  at  least  three  kinds  of  simple  proteids, 
combined  proteids,  extractives,  and  salts.  The  simple  proteids  are 
serum-albumin,  serum-globulin,  and  fibrinogen.  The  serum-albu- 
min is  separated  from  the  other  two  by  saturation  with  magnesium 
sulphate,  which  leaves  it  in  solution,  while  it  precipitates  the  glob- 
ulins. It  may  be  brought  down  in  a  neutral  or  acid  medium  by 
heat,  which  gives  three  different  coagulations :  at  73°,  77°,  and 
84°  C.  respectively,  indicating  three  kinds  of  serum-albumin.  In 
man  it  forms  about  4.52  per  cent,  of  the  solids.  Its  source  is  the 
absorbed  food-stuffs.  Serum-globulin  (paraglobulin)  is  coagulated 
at  75°  C.  In  man  it  forms  about  3.1  per  cent,  of  the  solids  pres- 
ent, and  is  more  abundant  in  serum  than  in  plasma,  on  account  of 
the  disintegration  of  the  white  blood-corpuscles,  which  takes  place 
during  coagulation.     Whether  this  is  its  sole  source  is  not  known. 

Fibrinogen  is  another  globulin  coagulating  at  from  56°  to  60°  C. 
It  is  present  in  human  blood  to  the  extent  of  0.22  to  0.4  per 
cent.  Its  nutritive  value  to  the  body  and  its  source  are  unknown. 
It  is  indispensable  to  the  coagulation  of  the  blood. 

Combined  Proteids. — These  are  hcemoglobin  and  nueleo-albumins. 

Extractives. — Such  include  substances  like  fats,  sugar,  urea, 
lecithin,  cholesterin,  and  gases. 

Inorganic  Salts. — These  are  peculiar  in  their  distribution,  inas- 
much as  the  plasma  contains  an  excess  of  sodium  salts  while  the 
corpuscles  contain  an  excess  of  potassium  salts. 

Coagulation  or  Clotting. — After  the  blood  has  escaped  from  the 
vessels  of  the  body  it  exhibits  its  most  peculiar  property — that  of 
clotting.  If  the  blood  is  caught  in  a  beaker,  it  is  at  first  perfectly 
fluid,  but  soon  becomes  viscous  and  sets  into  a  jelly.     As  the  clot 


liljxnt.  99 

shrinks  ill  size  it  presses  out  :i  clear.  I'aiiit-ycllow  liquid  called  blooil- 
scruin,  wliicli  incrca.si's  in  (|uantily  until  at  iliccnd  of  about  an 
hour  it  it;  sufKcicnt  in  amount  to  lloat  tlic  clot.  The  latter  becomes 
separated  from  the  .sides  of  the  ve.-NS*d.  The  appearance  ol"  the  clot 
or  cni-^.titntriit  u  III  y  dueto  the  formation  in  the  ]»lasma  of  fine  fibrils 
which  extend  in  every  direction  and  which  irradually  contract  and 
inclose  in  their  meshes  the  various  corpuscles.  The  process  may 
be  indicated  by  diagram  as  follows : 

Blood. 


Plasma.  Corpuscles. 


i  I 

Serum.  Fibrin. 

I 


Clot. 

_l 


Clotted  blood. 

When  coagulation  has  been  retarded  for  some  time,  the  red  cor- 
puscles have  time  to  sink  from  the  surface,  producing  after  coagu- 
lation a  yellow  layer  which  is  known  as  the  biiffy  coat.  Many 
leucocytes,  owing  to  their  amoeboid  movenients,  escai)e  from  the 
meshes  of  the  clot.  If  the  blood,  while  it  is  coagulating,  is 
agitated  with  a  bundle  of  rods,  the  filirin  is  removed  as  quickly 
as  it  is  formed,  and  appears  as  a  stringy  white  mass  on  the  rods. 
After  this  the  blood  appears  normal,  but  it  has  lost  its  power  to 
coagulate,  and  is  known  as  defibrinated  blood. 

The  value  of  clotting  is  that  it  stops  hemorrhage.  A  serious 
condition  is  present  in  some  pathological  states  where  the  blood 
will  not  clot.  The //wi^  of  c/o/^'/(7  varies  indifferent  individuals 
and  at  diilerent  times,  formally  the  jelly-stage  sets  in  in  from 
three  to  ten  minutes,  while  the  formation  of  serum  requires  from 
ten  to  forty-eight  hours. 

Owing  to  the  complexity  of  the  blood,  the  investigations  as  to 
the  cause  of  clotthig  have  given  rise  to  many  different  views.  It 
seems  to  be  well  established,  however,  tliat  the  formation  of  fibrin 
depends  upon  the  interaction  of  two  factors — the  fibrin  fennoif 
(fhroiiibi)i )  and  fibrliioijeii.  The  latter  is  not  entirely  used  up  in 
the  formation  of  fibrin  fonly  60  to  S>0  per  cent.),  but  a  portion 
aj)pears  in  the  serum  as  a  new,  globulin-like  proteid  called yi^nn- 


100  BLOOD  AND  LYMPH. 

globulin.  Calcium  salts  are  absolutely  essential  in  order  that  this 
reaction  may  take  place.  Their  exact  behavior  is  still  under  dis- 
cussion. It  has  been  stated  that  the  disintegration  of  leucocytes 
and  blood-jilates  in  the  blood  sets  free  a  nucleo-albamin,  which  may 
be  considered  the  precursor  of  the  ferment  and  called  prothrombin. 
Prothrombin  unites  with  calcium  to  form  the  ferment,  which  has 
the  power  of  reacting  with  a  portion  of  the  fibrinogen  molecule  by 
transferring  its  calcium  to  it  and  so  giving  rise  to  fibrin.  Fibrin 
ferment  was  originally  prepared  by  subjecting  serum  to  an  excess 
of  alcohol,  which  coagulated  the  proteids.  The  latter  were  re- 
moved and  extracted  with  water.  Such  preparations  were  found 
to  coagulate  fluids  like  hydrocele  liquid,  which  normally  do  not 
clot  spontaneously  or  at  least  very  slowly.  The  nature  of  the 
action  was  believed  to  be  that  of  an  enzyme,  since  very  small 
quantities  produced  great  changes,  and  it  was  destroyed  perma- 
nently by  heating  to  60°  C.  By  allowing  the  blood  to  run  from 
the  vessels  directly  into  alcohol  it  was  found  that  the  ferment  is  not 
present  in  normal  blood ;  that,  moreover,  it  has  its  origin  in  the 
leucocytes  is  shown  by  the  following  facts  : 

1.  In  microscopic  preparations  of  coagulating  blood  the  fibrin 
fibrils  radiate  from  broken-down  leucocytes  and  from  blood-plates. 

2.  Whatever  prevents  the  disintegration  of  the  white  blood- 
cells  retards  the  coagulation  of  the  blood. 

Clotting  within  the  blood-vessels  may  be  brought  about  by  the 
presence  of  foreign  bodies  or  by  injury  to  the  epithelial  lining  of 
the  vessels.  A¥heu  the  clot  is  confined  to  the  injured  area,  it  is 
called  a  thrombus.  General  intravascular  clotting  is  brought  about 
by  the  injection  of  fibrin  ferment,  nucleo-albumins,  etc.,  but  this 
is  not  accomplished  easily,  owing  to  a  defensive  function  for  the 
body  exerted  by  the  cells  of  the  liver.  Sometimes  the  blood  is 
rendered  less  coagulable  by  the  injection  of  the  above  substances, 
constituting  the  negative  phase  of  the  injection.  This  is  explained 
by  the  assumption  of  the  predominance  of  histon  over  leuconuclein, 
both  of  which  are  formed  by  the  breaking  down  of  leucocytes. 
Histon  retards  the  coagulation,  while  leuconuclein  favors  it.  Nor-  • 
mally  the  blood  of  the  body  is  prevented  from  clotting  by  the 
integrity  of  the  lining  epithelium  of  the  vessels.  In  the  living 
test-tube  experiment,  for  example,  the  jugular  vein  with  its  con- 
tained blood  are  removed  from  the  neck  of  the  horse,  and  it 
is  found   that   the    blood    under  these   conditions    remains  fluid 


liLOOD.  101 

until  tlu'  epithelial  cells  of  tiu'  Mood-vesst-ls  undergo  degenera- 
tive cluinged. 

If  M  not  known  wlidt  jterccnttKji'  of  h/oud  unnj  he  lost  bij  man 
thromjh  hcmorrluKje  witlioKt  Jatal  rrsiiUn,  hut  Jinlyintj  from  fxjtrri- 
niintu  upon  lower  animals,  if  may  be  jnit  at  about  -i  per  cent,  of  the 
boil  I/- weight,  or  one-fourth  of  the  total  blood. 

Reijeneration  of  the  blood  takes  place  rapidly  and  is  completed  in 
from  twenty-tour  to  tbrty-eight  hour.s.  xVt'ter  severe  homorrhafre 
recovery  is  more  certain  if  a  solution  of  so<liuni  chloride,  isotonic 
with  the  hlood  (O.i'  per  cent.)  in  man,  is  injected  into  the  veins. 
The  salt  solution  increases  the  blood-jirrs.fure  and  makes  rfj'rrfive 
the  remainini;  blond-corjtusclrs,  which  in  normal  blood  are  always 
in  exeess  of  the  number  absolutely  recjuired  tor  rrspirafori/  purposes. 

The  injeetion  of  saline  solutiou  iuto  the  blood-vessels  of  a  normal 
animal  raises  the  blood-pressure,  but  never  above  180  mm.  Hg. 
This  limit  holds  true  also  when  the  pressure  has  previously  been 
lowered  i)y  hemorrhaire  or  by  section  of  the  cervical  cord.  The 
explanation  of  this  fact  lies  in  the  manner  in  which  the  heart  is 
ati'ected.  As  soon  as  the  arterial  tension  reaches  its  maximal 
heiirht,  the  heart  beats  slower  and  less  vigorously,  and  the  re- 
sidual blood  in  the  left  ventricle  increases.  This  causes  a  diastolic 
rise  of  pressure  in  the  ventricle,  which  is  propagateil  back  through 
the  left  auricle,  pulmonary  circuit,  right  heart,  to  the  veins. 
There  arises  in  this  way  a  congestion  of  the  veins  and  capillaries 
of  the  lungs  ami  abdominal  organs  chiefly.  An  amount  of  salt 
solution  ecjual  to  four  times  the  nornial  quantity  of  blood  of  the 
animal  may  in  this  way  be  accommodated.  The  liver  becomes 
hard,  tense,  and  swollen,  and  other  tissues  become  (edematous. 
Owing  to  the  transudation  of  fluid,  the  ])ody  becomes  dropsical. 
The  bladder  is  distended  with  urine,  and  the  stomach  and  intes- 
tines become  filled  out  with  fluid.  These  factoi'S  prevent  the 
]>lood-pressure  from  rising  much  above  the  normal.  After  the  in- 
jection the  arterial  and  venous  pressures  return  quickly  to  the 
normal,  generally  within  an  hour.  Injection  of  saline  solution 
iliffers  from  transfusion  of  blood  in  that  in  the  former  case  the 
blood-flow  is  accelerated.  The  solution  injected  must  be  isotonic 
with  the  blood  of  the  animal,  of  the  same  temjierature.  and  every 
precaution  taken  to  |)revent  the  entrance  of  air.  When  injection 
of  salt  solution  is  maintained  for  some  time,  the  work  of  the  heart 
is   increased,  and   cardiac  failure  somi-times  results.      In  the  en- 


102  BLOOD  AND  LYMPH. 

deavor  to  avoid  the  latter  it  has  been  found  that  blood-letting 
rapidly  reduces  arterial  pressure,  owing  to  a  general  paralysis  of 
the  vasomotor  apparatus  through  overdistention,  so  that  the  ani- 
mal is  easily  killed  by  the  hemorrhage.  One  hundred  and  fifty 
per  cent,  of  the  normal  quantity  of  blood  of  the  animal  is  the 
maximal  amount  that  can  be  injected  without  directly  endanger- 
ing the  life  of  the  animal. 

Transfusion  of  blood  is  dangerous  for  two  reasons : 

1.  Strange  blood,  even  after  defibrination,  carries  an  excess  of 
fibrin  ferment  liable  to  cause  intravascular  clotting. 

2.  The  blood  of  one  animal  has  a  globulicidal  action  and  toxic 
effect  on  the  corpuscles  of  another.  By  globulicidal  action  is 
meant  that  property  of  the  serum  of  an  animal  which  causes  it  to 
destroy  the  red  corpuscles  of  the  blood  of  another,  thereby  ren- 
dering it  laky.  The  white  corpuscles  may  be  destroyed  as  well. 
As  an  example  it  may  be  said  that  man's  serum  is  globulicidal  to 
rabbit's  blood.  Similarly  the  blood  of  one  animal  may  be  poison- 
ous to  that  of  another  aside  from  its  globulicidal  action.  Thus 
the  injection  of  10  c.c.  of  dog's  serum  will  rapidly  kill  a  rabbit. 
These  properties  are  destroyed  if  the  blood  is  heated  to  60°  F., 
and  they  may,  as  has  been  suggested,  be  the  result  of  a  proteid 
substance — an  alexine — which  is  present  in  small  quantities  in  the 
blood  of  every  animal. 

LYMPH. 

Lymph  is  a  pale,  straw-colored  liquid  found  in  the  extravascular 
spaces  and  lymph-vessels  of  the  body,  bathing  every  tissue-ele- 
ment. It  is  slightly  alkaline,  of  a  salty  taste,  and  has  ??o  odor. 
It  contains  a  number  of  leucocytes ;  after  meals,  fat-globules ; 
accidentally,  red  corpuscles  and  blood-plates.  Lymph  contains 
the  three  blood-proteids,  the  extractives,  and  the  salts.  The  last  are 
in  the  same  proportions  as  in  the  blood  ;  the  proteids,  especially 
the  fibrinogen,  are  in  lesser  amounts.  Lymph  coagulates  more 
slowly  and  less  firmly  than  blood.  During  digestion  there  is  a 
marked  increase  of  fats  in  the  lymph  of  the  intestines,  making  it 
resemble  milk,  and  it  becomes  known  as  cJiyle.  The  lymph  de- 
rives substances  from  three  sources — from  the  blood,  from  the  tissues, 
and  from  the  villi  of  the  intestines.  It  is  first  collected  into  capil- 
lary spaces,   which   open  into    definite    lymphatic  vessels  which 


Ql'KSTIOyS   ON   VlIM'Tim    VII.  lO.'i 

tiually  empty  their  couteiits  into  the  hlood-ve.ssels  at  the  junetiou 
of  the  siihehivian  and  internal  jii<,Mihir  veiii.s.  The  eontinnal 
Ibrniation  of  lymph,  aided  by  sui)sidiary  forces,  leads  to  a  rela- 
tively hijjjh  |)re.ssure  in  the  lymph-spaces,  which  drives  the  lym[)h 
to  the  veins  or  points  of  lowest  pressure.  Among  the  Kiihsidiary 
forces  may  he  meuti<jne(l  the  j)umj)-aetion  of  the  villi,  the  peris- 
taltic movements  of  the  intestine,  and  the  action  of  the  skeletal 
muscles  in  contracting  and  the  pressure-changes  in  the  chest  <luring 
respiration. 

The  formation  of  lymi)h  from  the  blood  is  Itrought  al)out  mainly 
i)V  tiltration  and  osmosis.  The  endeavor  to  prove  the  jKtrticlpdtlon 
of  the  active  epithelial  cell  has  )i(>t  been  succexiifiil.  The  capilla- 
ries, however,  in  different  regions  of  the  body  have  a  different 
structure,  which  is  not  optically  recognizable,  but  which  gives 
them  different  permeabilities,  so  that  they  influence  the  character 
of  the  lymph  formed,  particularly  in  regard  to  the  percentage  of 
proteids. 

QUESTIONS  ON  CHAPTER  YII. 

How  docs  excessive  hemorrhaKe  affect  man  ? 

Wliat  is  the  function  of  the  l)loo(l? 

What  is  the  total  quantity  in  the  body  of  man? 

How  (Iocs  the  quantity  vary? 

How  is  the  total  <|uantity  of  an  animal  estimated? 

How  is  the  hloml  distrihutcil  in  tlie  body? 

What  arc  I  lie  compoiiciits  of  the  l)lood? 

What  is  the  cause  of  the  difference  in  colir  in  arterial  and  venous  blood? 

What  makes  the  blood  opaque? 

What  is  laky  blood? 

Give  the  physical  and  chemical  properties  of  blood. 

Discuss  the  corpuscles  of  the  blood. 

What  is  ha'in(ij,'lobin  ?     How  is  it  held  in  the  corijuscle? 

What  is  huMnochromorjcn  ? 

What  is  the  total  area  whicli  the  red  corpuscles  expose  to  tlie  action  of  the 
air? 

Discuss  some  of  the  comiiouiids  formed  by  luenioirlobin  and  various  jjases. 

Explain  why  illuiniiiatint;  <,'as  is  danj^'crous  wiicn  iiihalc<l. 

Wliat  is  the  perciMitane  of  iron  in  liiemoiflobin  ? 

Dcsi-ribe  the  crystiils  of  ha'moj,'l(ibin  and  their  maniK'r  of  jn-epanition. 

Wliat  are  ha^min  crystals?  How  prepared?  Of  what  importance  are 
they  ? 

Discuss  the  absorption  spectra  of  oxyha'tno^jlubin  and  of  reduced  ha-mo- 
globin. 

What  facts  indicate  that  red  corpuscles  remain  in  the  vessels  but  a  limited 
time  ? 

What  is  lia'mMtc>|ioiesis? 

Win  re  are  red  (■iiri)ns(lcs  formed?     Describe  the  process. 

How  are  the  white  blood -cells  cla.ssilied? 


104  CIRCULATION. 

What  is  diapedesis  ? 

What  is  the  function  of  leucocytes? 

Discuss  the  blood-plates. 

Describe  the  plasma  of  the  blood. 

By  what  methods  may  plasma  be  obtained  free  from  corpuscles? 

Explain  the  effect  of  the  injection  of  peptones  into  the  blood  of  an  animal. 

Why  do  oxalate  solutions  affect  coagulation  ? 

What  are  the  chemical  constituents  of  plasma? 

Give  the  percentage  of  serum-albumin  in  the  blood  of  man.  How  is  it 
separated  from  the  globulins  ? 

What  facts  indicate  that  there  is  more  than  one  kind  of  serum-albumin. 

What  is  the  percentage  of  serum-globulin  in  the  blood?  Give  its  probable 
source. 

What  is  the  percentage  of  iibriuogen  in  the  blood  ? 

What  substances  are  included  under  extractives? 

What  peculiarity  in  the  distribution  of  salts  in  the  corpuscles  and  in  the 
plasma  ? 

Describe  the  process  of  clotting. 

How  is  the  buffy  coat  produced? 

Give  the  chemistry  of  clotting. 

How  is  fibrin  ferment  obtained? 

How  has  it  been  shown  that  fibrin  ferment  is  normally  not  present  in  the 
blood  ? 

Give  proof  as  to  the  origin  of  the  fibrin  ferment. 

How  may  intravascular  clotting  be  produced  ? 

Explain  the  "negative  phase "  produced  by  the  injection  of  ferment  into 
the  vessels  of  an  animal. 

What  experiment  shows  that  the  epithelial  lining  of  the  vessels  normally 
prevents  clotting  of  the  blood  ? 

How  much  blood  may  be  lost  without  fatal  results  ? 

Why  is  the  injection  of  sodium  chloride  solution  beneficial  after  severe 
hemorrhage  ? 

Why  is  the  transfusion  of  blood  dangerous? 

What  is  meant  by  the  globulicidal  and  toxic  actions  of  the  blood? 

What  is  defibrinated  blood  ? 

Give  the  composition  and  the  physical  properties  of  the  lymph. 

What  is  chyle  ? 

What  is  the  source  of  lymph  ? 

What  forces  cause  the  lymph  to  flow  into  the  blood-vessels? 

To  what  extent  do  the  capillaries  influence  the  composition  of  the  lymph  ? 


CHAPTER  VIII. 

CIRCULATION. 

THE  HEART. 

The  blood  is  forced  through  the  vessels  that  contain  it  mainly 
by  the  rhythmic  contractions  of  the  heart.  Its  path,  in  general,  is 
as  follows :     Beginning  with  its  exit  from  the  left  ventricle  it 


THE   llEMir.  105 

]iasscs  into  llio  aorta,  ami  tlinmirli  its  varidiis  hranchcH  is  ra|)i<lly 
taken  iiild  the  systi'inic  capillaries  ot"  all  portions  ut"  the  liody. 
I'roin  the  capillaries  it  is  passe<l  into  the  veins,  which  lead  it  hack 
to  the  riiiht  anricle,  throui^h  w  hich  it  passes  to  the  ri;rht  ventricle. 
The  latter,  in  turn,  forces  it  throufj^h  the  arteries,  capillaries,  and 
veins  ot'thc  pulmonary  systi-rn  to  the  left  anricle,  and  then  to  the  left 
vrntriclc,  tlins  rcacliinL;'  its  starting-point.  That  ])ortion  of  the 
iilood  which  happens  to  pass  into  the  capillaries  of  the  stomach, 
intestines,  spleen,  or  pancreas  necessarily  circnlates  through  a 
second  set  of  capillaries  which  are  found  in  the  liver.  Living  rise 
to  what  is  known  as  the  ])ortal  circulation.  The  kidney  exhihits 
a  somewhat  similar  arranirement. 

Ecerii  particle  of  blood  follows  a  path  irliich,  )to  matter  hoic  de- 
viating it  may  he,  finally  returns  into  itself.  The  blood,  moreover, 
is  flowin«^  always  in  a  certain  definite  direction.  This  is  the  mean- 
ing of  the  expression  ''  circitlation  of  the  blood.^^  The  left  side  of 
the  heart  forces  the  hlood  through  the  systemic  vessels,  while  the 
right  side  forces  it  through  the  vessels  of  the  lungs.  It  is  thus 
possible  for  the  blood  to  carry  the  food-stutis  absorbed  from  the 
intestines  and  those  brought  to  it  by  the  thoracic  duct,  as  well  as 
the  oxygen  which  is  absorbed  in  the  lungs  to  all  the  cells  of  the 
body.  In  addition  it  carries  the  waste-products  of  the  cells,  in 
order  that  they  may  be  removed  by  the  proper  excretory  organs. 

The  energy  of  the  contractions  of  the  heart  is  derived  from  the 
potential  chemical  energy  of  the  food-stuffs,  and  is  entirely  con- 
verted into  heat  before  it  leaves  the  body.  Each  contraction  is 
technically  known  as  a  systole,  and  each  relaxation  as  a  diastole. 
During  the  .-iydolcs  of  the  rentrirlt-s,  which  occur  .simultaneously, 
the  bloixl  is  forced  into  the  arteries,  because  the  cavity  of  the  ven- 
tricles is  diminished  in  size,  and,  as  the  auricnlo-ventricular  valves 
are  closed,  the  blood  must  pass  through  the  open  semilunar  valve.'i. 
During  diastole  the  semilunar  valves  are  closed,  preventing  the 
regnrgitation  of  the  blood  from  the  <irfcries,  but  the  auriculoven- 
tririilar  valves  are  now  open,  so  that  the  blood  in  the  large  veins 
and  in  the  auricles  can  enter  the  ventricles. 

By  ex|)eriment  on  a  dog  it  has  been  found  that  blood  can  pass 
from  a  point  in  the  external  jugular  through  the  right  cavities  of 
the  heart,  aorta,  arteries,  capillaries  and  veins  of  tlie  head  to  the 
starting-point  in  fifteen  to  eighteen  seconds.  Each  contraction  and 
relaxation  or   beat  of  the   heart  consists  of  a  regular  sequence  of 


106 


CIRCULATION. 


events  known  as  the  cardiac  cycle.  The  systoles  of  the  two  auri- 
cles occur  together,  as  do  those  of  the  ventricles,  and  the  same  is 
true  of  their  diastoles.  While  the  auricles  are  contracting  they 
shrink  in  size,  and  at  this  time  the  ventricles  swell.  Then  follow 
immediately  the  systoles  of  the  ventricles,  during  which  the  ven- 
tricles diminish  in  size,  the  auricles  swell,  and  the  injected  arteries 
grow  larger  and  longer.  During  the  succeeding  diastoles  of  the 
ventricles  both  ventricles  and  auricles  swell  until  the  next  contrac- 
tion of  the  auricles  swells  the  ventricles  still  more.    These  changes 


Diagrams  of  valves  of  the  heart  (after  Dalton). 


in  the  size  of  the  heart  are  due  entirely  to  the  varying  amounts  of 
blood  contained,  and  not  to  any  variations  in  the  hulk  of  the 
heart-muscle.  In  the  relaxed  condition  the  heart-walls  are  very 
soft  and  flaccid.  Owing  to  this  fact  the  changes  of  form  that  the 
heart  undergoes  are  easily  modified  by  gravity  when  the  thorax 
is  opened  and  the  heart  exposed,  since  it  is  then  unsupported  by 
the  lungs,  which  normally  have  a  dilating  influence.  In  this  con- 
dition in  an  animal  lying  on  its  back  it  is  seen  that  during  a  con- 
traction of  the  ventricle  the  long  axis  of  the  heart  sweeps  toward 
the  median  line,  and  also  toward  the  head,  so  that  the  apex  rises  a 


THE  11  EMIT.  107 

little  toward  the  ohserver.  Tlie  heart  twists  so  thnt  the  left  ven- 
tricle inovevS  nearer  the  breast,  while  the  rii^ht  turns  toward  the 
spine.  There  is  no  cIihikjc  of  color  in  the  ventricle,  hut  the  ou- 
rieleH  being  thin,  show  the  blood  within — the  right,  bliiiili ;  the 
left,  br'ujht  red.  As  the  auricles  contract  they  heeonie  |)aler.  A 
distinct  puUe  is  present  in  the  arteries,  hut  none  in  the  veins.  In 
the  unopened  client  it  is  probable  that  the  ventricles  become 
smaller  in  girth  during  systole,  and  that  they  are  always  approxi- 
mately circidar  and  not  elliptical.  The  ventricles  shorten  .some- 
what in  length,  but  the  apex  does  not  leave  the  chest-wall,  because 
the  injected  arteries  at  the  biuie  of  the  heart  lengthen  and  i)ush 
the  entire  heart  forward  thus  fully  comi)ensating  for  the  shorten- 
ing of  the  ventricle.  The  apex  of  the  heart  as  it  coutractij 
hardens,  and  i)rotrudes  the  chest-wall  in  the  intercostal  space  of 
the  fourth  and  fifth  ribs,  midway  between  the  left  margin  of  the 
sternum  and  a  vertical  line  let  fall  from  the  left  nipple.  This 
constitutes  the  impure  or  apex-beat,  and  it  coincides  with  the  uj)- 
stroke  of  the  pulse.  Around  the  protrusion  caused  by  the  apex- 
beat  the  soft  parts  of  the  che.^t-wall  are  drawn  in  slightly,  wliich 
is  tlue  to  the  fact  that  the  heart  becomes  smaller  at  that  time,  and 
is.  therefore,  in  contact  with  the  chest-wall  over  a  smaller  area. 
This  drawing-in  is  called  the  negative  impulse. 

The  heart  during  each  cycle  produces  two  sounds.  The  first, 
low-pitched  and  muttled,  coi)icides  with  the  .•<jisfoles  of  the  ventricles, 
and  is  therefore  hearil  when  the  apex-beat  is  felt.  The  .second 
sound  is  shorter,  higher,  and  clearer  than  the  other,  and  follows 
after  a  scarcely  appreciable  interval.  It  coincides  with  the  early 
part  of  the  diastole  of  the  ventricle.  After  the  second  sound  there 
is  a  period  of  silence,  which  is  coincident  with  the  latter  portion  of 
the  diastole  of  the  ventricle  and  the  si/stole  of  the  auricles.  It  has 
been  proved  that  the  second  sound  is  due  to  the  closure  of  the 
semilunar  valves  of  the  pulmonary  artery  and  the  aorta.  When 
these  are  ex})erimentally  rendered  incompetent,  the  second  sound 
disappears  and  is  replaced  by  a  murmur.  The  first  sound  is  be- 
lieveil  to  be  due  to  the  combined  action  of  the  closure  of  the  tri- 
cuspid and  mitral  valves,  and  by  the  muscle  sound  produced  by 
the  ventricles  in  contracting.  The  first  souml  is  heard  best  over 
the  a|)ex  of  the  heart.  The  closure  of  the  tricuspid  valve  can  be 
listened  to  be.st  at  the  lower  end  of  the  sternum.  The  second 
souml  is  heard  best  at  e^ich  side  of  the  sternum,  between  the  first 


108  CIBCULATIOK 

and  second  ribs,  being  propagated  upward  along  the  great  vessels 
to  which  the  semilunar  valves  are  attached. 

The  average  rate  of  heart-beat  in  an  adult  man  is  about  72  a 
minute,  and  is  somewhat  faster  in  women.  It  varies,  however,  so 
that  in  some  individuals  it  may  be  40  or  100  a  minute.  Shortly 
before  and  after  birth  it  averages  from  120  to  140.  During  ex- 
treme age  its  frequency  is  increased.  It  is  influenced  by  many 
conditions  of  bodily  health  and  environment,  such  as  sleejj,  position, 
temperature,  meals,  and  emotions.  Exercise  may  increase  it  to  200 
or  more. 

The  auricular  systole  is  rapid,  and  forces  the  blood  into  the  still 
quiescent  ventricles.  On  completion  of  the  auricular  systole  the 
auricles  expand  and  remain  quiet  during  the  systole  of  the  ventri- 
cles, which  begins  the  moment  the  auricles  cease  contracting.  The 
ventricular  systole  is  more  forcible  than  that  of  the  auricles,  and 
they  remain  longer  in  a  contracted  state.  During  ventricular  sys- 
tole the  blood  is  forced  into  the  arteries.  At  the  close  of  the  ven- 
tricular systole  the  ventricles  dilate.  The  auricles  do  not  take  up 
the  w^ork  again  at  once,  but  there  is  a  period  during  which  the 
entire  heart  is  in  repose.  After  this  a  new  cycle  is  begun.  If  we 
assume  the  average  number  or  heart-beats  to  be  72  a  minute,  each 
cardiac  cycle  occupies  0,8  of  a  second.  The  contraction  of  the 
auricles  lasts  0.1  of  a  second  ;  that  of  the  ventricles,  0.3  of  a  sec- 
ond ;  and  the  repose  of  the  entire  heart,  0.4  of  a  second.  If  the 
heart-rate  be  increased,  the  ventricular  systole  remains  about  0.3 
of  a  second,  and  the  increase  in  rate  is  made  at  the  expense  of  the 
time  occupied  by  the  diastole. 

It  is  the  function  of  the  heart  to  force  the  blood  in  one  direction 
only,  and  this  is  effected  by  means  of  the  valves.  As  the  ventricle 
fills,  the  auriculoventricular  valves  are  floated  up  from  the  sides 
of  the  ventricle  in  such  a  manner  that  their  edges  are  brought  into 
contact.  As  the  ventricle  contracts  more  forcibly  pressure  is 
brought  upon  the  valves,  so  that  not  only  are  the  edges  in  contact, 
but  also  portions  of  the  surfaces  of  the  cusps.  These  valves  are 
of  considerable  area,  and  are  held  in  position  by  the  chordce  ten- 
dime,  which  arise  from  the  papillary  muscles,  so  that  eversion  of 
the  valve  into  the  auricle  is  impossible.  The  semilunar  valves 
form  a  guard  against  the  return  of  the  blood  to  the  ventricle  at 
the  pulmonary  and  aortic  openings.  These  valves  are  forced 
open  during  the  ventricular  contraction  by  the  blood  which  passes 


TIIJ-:  HEART. 


lUU 


thr()U,t,'h  them  to  distend  the  ehustic  \\^\U  of  tlie  hirge  arteries. 
The  i)re.ssuie  ol"  the  hiood  under  the  rladic  recoil  iri  «uHieient  to 
throw  the  euspri  of  the  viilves  into  action.  The  rorjioni  Aruiitii 
are  useful  in  making  a  perfect  closure  of  the  valve,  although  uot 

Fig.  9. 


Ludwig's  stromuhr  and  ft  diagrammatic  representation  of  the  same.  This  con- 
sists of  two  glass  bulbs,  ,1  and  B,  coranninicating  above  witli  each  other  and  with 
the  common  tube  <\  by  which  they  may  be  filled.  Their  lower  ends  are  fixed  in 
the  metal  disc  I),  which  may  be  made  to  rotate,  through  two  right  angles,  around 
(he  lower  disc  E  In  tlie  u)>per  disc  are  two  holes,  a  and  h,  continuous  witli  .1  and 
li  respectively,  and  in  the  lower  disc  are  two  similar  holes,  n'  an<l  t)',  similarly  con- 
tinuous with  "the  tubes  G  and  //.  Hence,  in  the  position  of  the  discs  shown  in  the 
figure,  the  tube  O  is  contin\ious  with  the  bulb  .l,and  the  tube  //with  the  bulb 
li.  On  turning  the  disc  I)  thnmgh  two  right  angles,  the  ttibe  G  becomes  contin- 
uous with  B  instead  of  A,  and  the  tube  //with  .1  in.stead  of  B  (Foster). 


absolutely  essential.  A  part  of  the  weiirht  of  this  pressure  is 
borne  liv  the  thick  ventricular  wiill.  which  forms  a  rintr  from  the 
outer  edi^e  of  wliich  tlie  arteries  sprintr,  while  the  valves  are 
attaelied  to  the  inner  edire.  Under  some  circumstances  the  tricus- 
pid valve  does  not  entirely  close,  but  allows  a  certain  amount  of 


110  CIRCULATION. 

regurgitation  of  blood.  This  occurs  in  conditions  of  disease  or  of 
violent  exercise,  when  the  lung  capillaries  are  overcharged  with 
blood.  The  leakage  of  the  valve  is  conservative,  and  relieves  the 
pressure  upon  the  delicate  capillaries  of  the-  pulmonary  system. 
Pulsation  in  the  jugular  veins  indicates  this  regurgitation.  The 
condition  is  not  pathological,  and  with  altered  conditions  dis- 
appears. 

During  each  cycle  of  the  heart  there  is  ejected  from  the  ven- 
tricles a  quantity  of  blood  known  as  the  contraction  or  pulse  vol- 
mne.  It  varies  in  the  same  heart  at  different  times,  but  on  an 
average  must  be  equal  for  both  ventricles,  and  must  also  equal  the 
amount  that  enters  the  systemic  or  pulmonary  capillaries  during 
the  entire  cycle.  The  amount  may  be  roughly  measured  by  intro- 
ducing a  modified  stromuhr  between  the  origins  of  the  coronary 
arteries  and  of  the  innominates.  It  may  also  be  measured  by  en- 
closing the  heart  in  a  plethy sinograph.  It  has  been  estimated  for 
man  as  being  from  50  to  190  c.c.  If  its  weight  is  taken  at  100 
grammes  and  the  blood  in  an  average  man  weighs  about  5300 
grammes,  it  is  seen  that  the  pulse  volume  is  equal  to  about  one- 
fifty-third  of  the  entire  bloody  so  that  all  the  blood  of  a  person  passes 
through  the  heart  in  less  than  a  minute.  Each  pulse  volume  is  ' 
injected  into  the  arteries  against  considerable  resistance,  so  that  the 
ventricles  perform  work.  The  amount  of  work  may  be  calculated 
by  multiplying  the  weight  of  the  pulse  volume  into  the  force 
exerted  by  the  ventricles.  The  latter  is  equal  to  the  pressure 
under  which  the  pulse  volume  is  expelled.  This  pressure  may  be 
measured  in  animals  by  introducing  a  tube  through  the  external 
jugular  into  the  ventricle,  and  connecting  with  a  mei'cury  manom- 
eter pi'ovided  with  a  valve,  so  that  the  maximum  pressure  may 
be  recorded.  The  left  ventricle  exerts  more  than  twice  as  much 
power  as  the  right.  The  exact  intraventricular  pressure  in  man  has 
not  been  determined.  The  expansion  of  the  heaH  e.'s.evi^  a  negative 
pressure  which  aids  the  onfioiv  of  the  blood  especially  from  the 
lungs  to  the  left  auricle  and  ventricle.  The  intra-auricular  pres- 
sure is  very  much  less  than  the  intra-ventricular,  and  there  is  a 
negative  pressure  during  the  diastole  of  the  auricles.  It  has  been 
estimated  that  each  ventricular  contraction  equals  3}  to  4i  foot- 
pounds. In  twenty-four  hours  this  is  equal  to  more  than  120  foot- 
tons.  Practically  all  the  energy  of  the  heart's  contractions  is 
converted  into  heat  by  the  friction  of  the  blood  in  the  vessels. 


Tin-:  II EMIT. 


Ill 


Fiu.  10. 


V>\  i\  sHtrht  nltcratioii  dftlie  "niaxiimiin  nmnonieter  "  it  may  lie 
converted  into  one  lliat  records  ininiiiuini  pressures.  \\y  the  em- 
liloyineiit  of  .«iich  iiiatioinelers  it  lias  lieeii  a.scerlaiiied  upon  a  dog 
in  one  case  that  the  inaxinium  pressure  in  the  ventricle  rose  as 
hii^h  as  234  niui.  Hg.,  while  that  in  the  aorta  reached  212  mm. 
Iljr.  The  minimum  of  the  left  ventricle  was  minus  3H  mm.  lljr., 
wliile  that  of  the  aorta  did  not  jjet  lower  than  120  mm.  Hg.  These 
values  vary,  but  their  relations  to 
one  another  may  he  taken  as  an 
example  of  what  is  true  of  both 
ventricles.  It  is  seen  that  tlie 
jire«sure  in  the  artery  is  always 
hl(jh,  fluctuating  but  little,  while 
that  of  the  ventricles  rises  above 
the  highest  arterial  pressure  and 
falls  much  l)elow.  The  pressure 
of  the  blood  in  the  ventricle  must 
overcome  that  within  the  arti'ry 
to  open  the  semilunar  valves  and 
force  the  blood  into  the  artery. 
As  the  pressure  falls  in  the  ven- 
tricle the  semilunar  valves  close 
as  soon  as  it  is  less  than  that  of        ,  ,  ., 

,  1  i  -i.  hdrse  (after  riiaiivomi  aiui   Miircy): 

the  arterv,  and  prevent  regurgita-     «,o',  bofrinninf;  nfcaniiac  cycle : '',/*', 

tinn        WhpTi    tlie    nre=sure    in    the      rise  of  pressure  due  to  auricular  sys- 
tion.       >>  nen   ine    yiresbure    in    me      ^^^^,  ^.^  pressure  due  to  ventricular 

ventricles     is     at     its    lowest,     the      systole:  rf',  oscillations  due  to  inertia: 
,  ,       ,      ,  •       n  i.1       1  e,e',  close  of  cardiac  cycle. 

blood  streams  in   from   the   large 

veins  and  from  the  auricles,  because  the  pressure  in  the  latter, 

although  low,  is  higher  than  that  in  the  ventricle. 

Curves  of  endocardiac  pressure  which  are  obtained  by  inserting 
a  hollow  probe  into  the  various  chambers  of  the  heart  difter  in 
their  form  as  the  method  is  by  air  or  by  liquid.  Pressure-curves 
from  the  ventricle  transmitted  by  air  are  peaked,  the  pressure 
rising  swiftlv  to  a  m:iximum,  and  then  as  rapidly  falling  to  or 
below  atmosjiheric  pressure.  There  follows  then  a  slow  gradual 
rise  until  the  next  systole  of  the  ventricle.  Transmission  by  water 
gives  the  same  curve,  with  the  excejition  that  the  jieak  is  replaced 
by  a  plafirnt — /.  ^.,  the  pressure  instead  of  falling  after  reaching  a 
maximum  is  sustained  for  s(mie  time.  The  latter  is  ])robably  the 
truer  form  of  the  pressure  change.     The  fluctuations  of  the  plateau 


Simultnneous    tracings    from    the 
ri>;ht    auricle    and   ventricle    <if   the 


112  CIRCULATION. 

are  due  to  oscillations  produced  by  inertia.  An  endocardiac 
pressure-curve  very  rarely  shows  any  indication  as  to  the  play  of 
valves.  These  must  be  obtained  by  carefully  graduating  two  elas- 
tic manometers  and  connecting  them  with  auricle  and  ventricle, 
or  ventricle  and  aorta  respectively.  The  relative  pressures  are 
given  by  the  heights  to  which  the  recording  levers  rise,  and  thus 
the  closure  of  the  various  valves  may  be  ascertained.  As  long  as 
the  tricuspid  or  mitral  valves  are  open  the  pressure  in  the  ven- 
tricle is  lower  than  that  in  the  auricle,  and  the  blood  is  entering 
from  the  veins.  That  in  the  arteries  is  shut  out  by  the  closed 
semilunar  valves.  This  is  called  the  period  of  reception  of  the 
blood.  When  the  cuspid  valves  are  shut,  the  semilunar  valves 
are  open,  and  the  blood  is  being  forced  by  the  ventricle  into  the 
arteries.  This  is  the  period  of  ejection.  There  are  two  brief 
periods  of  complete  closure  of  the  ventricles — i.  e.,  when  both  cuspid 
and  semilunar  valves  are  closed.  When  the  ventricle  contracts 
upon  its  contained  blood  and  thus  raises  the  pressure,  the  cuspid 
valves  close  readily,  but  it  takes  some  time  for  the  pressure  to  be- 
come sufficiently  high  to  open  the  semilunar  valves.  Similarly 
when  the  ventricle  relaxes  the  high  pressure  in  the  arteries  closes 
the  semilunar  valves  immediately,  but  it  takes  some  time  for  the 
pressure  to  fall  low  enough  that  the  cuspid  valves  can  open. 
During  the  ventricular  diastole  at  the  time  when  the  cuspid  valves 
are  just  opening  the  blood  which  has  been  accumulating  in  the 
auricles  flows,  and  to  some  extent  is  drawn  into  the  ventricles. 
This  force  of  slight  suction  is  due  to  the  elastic  fibres  of  the  lung, 
which  tend  to  open  the  ventricles  and  also  to  the  elasticity  of  the 
heart-muscle  itself,  especially  of  the  auriculo-ventricular  ring. 
The  ventricles  can  maintain  the  circulation  of  the  blood  for  a  time 
at  least,  unaided  by  the  auricles.  The  latter  form  a  storehouse 
for  the  blood  which  accumulates  during  the  ventricular  systole. 
The  pressure  in  them  in  the  dog,  for  instance,  seldom  rises  above 
10  mm.  Hg.  They  form,  therefore,  but  a  feeble  force-pump 
which  completes  the  filling  of  the  ventricles.  Their  value  in 
this  respect  becomes  important  when  the  heart-rate  increases,  for 
then  the  ventricular  pause  is  shortened  and  the  auricles  form  an 
efficient  mechanism  for  quiclcly  charging  the  ventricles.  The  nega- 
tive pressure  of  the  auricles  has  been  found  to  be  as  low  as  minus 
10  mm.  Hg.  This  is  caused  by  the  elasticity  of  the  lung,  which 
just  at  this  moment  is  heightened  because  the  contracting  ventricle 


rilF.    UK  MIT.  113 

inri'i'dsrs  the  iH'ijafirc  ///vx-xj/rr  in  the  clir.4.  The  mouths  of  the 
t/mit  irin-f  enij)tyinji;  into  the  auricles  are  ititprorl^hd  with  culrcx, 
liiit  are  rich  in  circular  mnnclr-jihn-x  wliich,  by  their  contraction, 
ni:iv  obliterate  the  lumen  of  the  vessels  and  so  prevruf  rrfjnnjita- 
lion.  The  systole  of  the  heart  is  known  to  begin  with  tlie  veins, 
and  swee]>  down  over  the  auricles,  and  some  have  contended  that 
the  tlow  of  venous  blood  is  never  checked,  but  that  the  contracting 
vi'ins  and  auricles  carry  it  snioollily  into  the  ventricles  by  com- 
pensating l»y  tiicir  contraction  for  the  expansion  of  the  auricles 
and  ventricles  and  the  opening  of  the  cuspid  valves. 

The  aai.^e  of  the  rhijthiiiic  movements  of  the  heart  lies  within 
itself,  since  it  can  be  severed  from  the  central  nervous  system  with- 
out necessarily  destroying  its  activity.  For  some  time  many  ob- 
servers contended  that  the  rich  nerve-supply  was  essential,  but  it 
has  been  shown  that  many  forms  of  contractile  substance  may  be 
rhythmically  active.  A  strip  of  muscle  cut  from  the  apex  of  a 
tortoise's  heart,  which  contains  no  ganglion-cells,  and  suspended 
in  a  moist  chamber,  may  beat  as  long  as  thirty  hours  with  a  slow 
rhythm.  Very  small  microscopical  pieces  from  the  bulbus  aortas 
of  the  frog,  which  are  proliably  devoid  of  nerve-cells,  contract 
rhythmically.  Curarized  striated  muscle  placed  in  certain  saline 
solutions  will  show  a  regular  rhythm  for  hours.  Many  inverte- 
brates have  hearts  that  are  not  provided  with  nerve-cells.  The 
Jirarf  of  fhr  nnhn/o  hrafs  before  the  iierrex  Jiare  r/ro)r))  Into  if. 

The  canliac  contraction  is  preceded  by  a  change  of  electrical 
potential,  which  sweeps  over  it  in  the  form  of  a  wave.  Both  nor- 
mally take  the  same  course,  beginning  at  the  great  veins  and 
spreading  rapidly  over  the  auricles,  then  a  short  pause,  after 
which  they  spread  over  the  ventricles.  At  times  the  contraction 
may  originate  in  the  ventricle.  Thus,  by  drawing  a  tight  liga- 
ture about  the  heart  at  tlie  junction  of  the  auricles  and  ventricles, 
the  rhythm  of  the  b.eart  is  disturbed  and  the  ventricle  beats  with 
an  independent  slower  rhythm.  If  the  rJrctrienJ  cha)i(/e.<  of  the 
beating  heart  are  investigated,  it  is  found  that  the  base  becomes 
negative  before  the  apex,  and  that  this  condition  of  negative 
potential  pas.«es  along  in  the  form  of  a  wave  to  the  apex.  Its 
speed  has  been  found  to  average  at  lea.'Jt  50  mm.  a  second.  The 
/(iteiit  jtrriod  of  frog's  heart-muscle  is  about  0.08  of  a  second, 
but  the  change  of  potential  takes  place  instantly  after  the  applica- 
tion of  the  stimulus.  The  excitation  wave  can  be  made  to  paijS 
S— Phys. 


114 


CIRCULATION. 


Fig.  11. 


s.r 


/// 

DiacTammatic  representation  of  the  course  of  cardiac  auKmentor  fibres  in  the 
frng  (Foster) :  T'.r.,  roots  of  vagus  (and  ninth)  nerve,  r/.  T'.,  ganglion  of  same.  Cr., 
line  of  cranial  wall.  TV/.,  vagus  trunk,  ix.,  ninth,  glossopharyngeal  nerve, 
.s.  V.  C,  superior  vena  cava.  Sy.,  sympathetic  nerve  in  neck.  G.  r.,  junction  of 
sympathetic  ganglion  with  vagus  ganglion  .sending  i.  c,  intra-cranial  fibres,  passing 
to  Gasserian  ganglion.  The  rest  of  the  fibres  pass  along  the  vagus  trunk.  (Ji, 
splanchnic  ganglion  connected  with  the  first  spinal  nerve.  G",  splanchnic  gan- 
glion of  the  second  spinal  nerve.  ^?i.  T'.,  annulus  of  Vieussens.  yl.  «&.,  subclavian 
artery.  G'li,  splanchnic  ganglion  of  the  third  spinal  nerve.  III.,  third  spinal 
nerve,    r.  c,  ramus  communicans. 

The  course  of  the  augmentor  fibres  is  shown  by  the  thick  black  line.  They 
may  be  traced  from  the  spinal  cord  by  the  anterior  root  of  the  third  spinal  nerve, 
through  the  ramus  communicans  to  the  corresponding  splanchnic  ganglion  f?'". 
and  thence  by  the  second  ganglion  G^^,  the  annulus  of  Vieussens,  and  the  first 
ganglion  G^,  to  the  cervical  sympathetic  Sy,  and  so  by  the  vagus  trunk  to  the  supe- 
rior vena  cava  S.  V.  C. 


THE  in:.\i:r 


OJ. 


Fig.  r_'. 

niiiKrainnialic  reprcsenta- 
tiiin  i>l"  tlif  ciinliiil  iiiliiliitDry 
and  aiiKiiU'iitor  lil>ri-s  in  the 
i\i>ii.  '\'\w  uiipiT  |H>riii>n  >>(  ilie 
ti^'iiri'  ri'iircscnts  tlic  inliil>i- 
im-y,  the  luwor  the  iiunnK'nlor, 
lihrVs  I  Kosteri :  r.  l';/.,  roots  of 
the  \m;iis.  r.S]i..\i\,  roots  of 
siiiniil  iiceessory  :  hotli  tirawn 
very  iliiii^rununatieally.  (i..l., 
Kiin^'liiiii  jiij,'iilure.  (i.  'Jr.  \'(i'., 
unn^^Wiiu  trunci  vaji.  Sji.Ar., 
spinal  accessory  trnnlc.  cxt. 
>'/). .!<•.,  external"  spinal  acces- 
sory. i.Sii.Ar.,  internal  spinal 
accessory.  \'.<i..  lninl<  of 
va>;us  nerve.  ".''.,  l>ranelies 
troiliK  to  heart.  ('.Sy..  cervi- 
cal sympathetic.  G.C,  lower 
cervical  jran^jlion.  ^I..'--/).,  suli- 
clavian  arterv.  Aii.\'.,  annn- 
lus  of  Vieiissi'ns.  G.SI.  {T/i.h. 
f^anKlion  stellatuin  or  first 
thoracic  fian^'lion.  G.TIi.-, 
(i.rh?,  (;.rh.\  second,  third, 
and  fourth  thoracic  Kan.i,dia. 
I). 11..  I). III..  IKIV..  /^r.,  sec- 
ond, third,  fonith,  and  fifth 
thoracic  spinal  lU'rves  r.c. 
ramus  comniunicans.  n.c, 
nerves  (cardiac)  passing;  to 
heart  (superior  vena  cava) 
from  cervical  eannlion  and 
from  the  annulus  of  Vieus- 
sens. 

The  inhibitory  fibres, 
shown  by  black  line,  run  in 
the  upper  (medullary  roots) 
of  the  siiiiuil  accessory,  l>y  the 
internal  branch  of  the  spinal 
accessory,  i)ast  the  ganplion 
trunci  v'a^i,  alon^  the  trunk 
of  the  vagus,  and  so  by 
branches  to  the  sujierior  vena 
cava  and  the  lieart. 

The  au).cnientc)r  fibres, 
also  shown  \>\  black  line, 
pass  from  the  spinal  cord  by 
the  anterior  roots  of  Llie 
second  and  third  thoracic 
nerves  (i)f)Ssibly  also  from 
fourth  and  fifth  as  indicated 
by  broken  black  line),  i)ass 
the  second  and  first  (stellate) 
thoracic  nantilia  by  the  annu- 
lus of  Vieiissens  to  the  lower 
cervical  (;"nuH<>n,  from 
whence,  as  also  from  the 
annulus  itself,  they  juiss 
alone  the  cardiac  nerves  to 
the  superior  vena  cava. 


n.Tr.Vn 


11 


r.Vg. 


Sp.Ac. 


O.TliX 


116  CIRCULATION. 

over  the  heart  in  any  direction,  and  the  speerf  with  which  it  travels 
indicates  that  it  passes  through  muscle  and  not  througli  nerve. 
The  duration  of  the  pause  or  block  in  the  frog's  heart  has  been 
found  to  be  from  0.15  to  0.30  of  a  second.  The  speed  of  the  ex- 
citation-wave in  embryonic  muscle  (3  to  11  meters  a  second) 
makes  it  plausible  that  in  the  lieart  the  block  is  due  to  the  fact 
that  the  excitation-wave  is  transmitted  through  embryonic  muscle- 
fibres  that  exist  between  the  auricle  and  ventricle.  It  is  found 
that  when  a  heart  is  subjected  to  a  series  of  stimuli  it  will  respond 
regularly  when  the  rate  is  slow,  but  when  it  becomes  too  rapid,  the 
stimuli  will  not  all  be  able  to  call  forth  a  response.  The  heart- 
muscle  loses  its  irritability  during  a  part  of  its  systole,  and  regains 
it  during  the  remainder  of  the  systole  and  the  following  diastole. 
During  a  part  of  the  cardiac  cycle,  therefore,  it  is  refractory  to 
stimuli.  A  stimulus  falling  within  the  refractory  period  is  without 
effect.     A  stimulus  falling  within  the  non-refractory  period  calls 

Fig.  13. 

l/\/lA/\/W\/L_.yvAAAA. 

Effect  of  stimulation  of  pneumogastric  nerve  upon  action  of  heart  in  frog.    To  be 
read  from  left  to  right  (Chapman). 

out  a  contraction,  but  does  not  disturb  the  rhythm  of  the  heart, 
because  it  is  followed  by  a  pause  of  extra  length.  This  is  called 
the  compensatory  jmuse.  The  first  systole  after  an  extra  contrac- 
tion and  a  compensatory  pause  is  of  marked  strength. 

The  nerves  of  the  heart  are  branches  of  the  vagus  and  the 
syvijMthetic.  Some  of  the  fibres  of  the  vagus  which  are  derived 
from  the  spinal  accessory  terminate  in  end-baskets  which  surround 
sympathetic  ganglion-cells  whose  axis-cylinder  processes  end  on 
the  muscle-fibres.  Other  fibres  of  the  vagus  end  in  end-brushes 
in  the  pericardium  and  endocardium.  Fibres  of  the  sympathetic 
system  arise  from  cells  in  the  cord  and  pass  out  through  the  white 
rami,  ending  in  the  inferior  cervical  and  stellate  ganglia  on  cells 
whose  axis-cylinder  processes  in  turn  pass  either  directly  to  the 
heart-muscle  or  to  a  third  neuron  lying  in  the  heart. 

Stimulation  of  the  vagus  fibres  along  any  portion  of  their  path 
from  the  medulla  to  the  heart  inhibits  the  heart's  action.     The 


77/a;  ii/Airr 


117 


eHW't  is  not  iinnuMlinte,  l)ut  follows  u  latent  periofi  which  oxteuds 
oviT  a  lu'at  or  (wo.  The  inlilhifion  inanifi'sts  itself  at  first  hy  a 
leii;.ftheiiiii<;  of  the  duralioii  of  (he  diaslole  without  any  ehanjre  in 
the  systole.  A  stronj,aM- sdniulation  lengthens  the  .systole  also,  and 
may  stop  the  heat  of  the  heart  altogether.  Inhibition  is  further 
xlioH'tt  hy  a  /('xsniinf/  oi'  the  force  of  the  (•otilraction  ;  by  an  increase 
of  ]>reKKurt'  in  the  lieort  during  diastole;  \)\  on  increase  in  the 
amount  of  residual  blood ;  hy  a  decrease  in  the  injtiit  and  oiifjtitt 
of  the  ventricle,  and  hy  diminished  ventricular  tonus.  It  inav 
further  he  said  that  during  vagus  excitation  the  j)roj)agati(«i  of 
the  cardiac  excitation  is  more  ditiicnlt.  A  demarcation  current 
tlerived  from  a  jMjrtion  of  the  auricle  is  increased  by  var/us  excita- 
tion, although  the  auricle  shows  no  visible  change  of  form.  The 
heart  cannot  be  continuously  inhibited  by  prolonged  stimulation. 

Fig.  14. 


'y.vA\z\\\z%%mmwMmmwmm/immm'aiivMMmmMv^ 


Effect  produced  by  stimulatidU  f)f  ]<  ripliernl  cml  nf  tlu'  iKcvliintiriK  iutvl'  of  the 
heart.    The  licart  beats  mure  quickly.    Stiimilatiuii  begun  at  >'  ^LaudoJs). 


It  e-scajies  from  the  influence  of  the  vagus  and  resumes  its  former 
rhythm  with  perhaps  increased  force.  Immediate  stitnulafiini  of 
the  second  r«7».*i  after  the  heart  has  escaped  from  the  influence  of 
the  first  is  without  effect,  making  it  probable  that  both  uerve.<  act 
upon  the  same  mechanism  in  the  heart. 

Stimulation  of  the  siimj»athetic  or  augmevtor  fibres  causes  an  in- 
crea.se  in  the  rate  of  the  heart-beat  from  7  to  70  per  cent.,  the 
amount  of  increase  de]HMiding  upon  the  heart's  rate  before  stimu- 
lation. A  lonff  excitation  jiroduces  no  (jreater  acceleration  than  a 
sfitirt  one.  The  force  of  the  beat,  the  pjilse-ndume,  and  the  sj)erd 
i)f  the  e.rcitation-u'ave  are  all  increased.  The  latent  ])eriod  is 
usually  a  long  one,  extending  from  two  to  ten  seconds.  The  accel- 
eration may  continue  for  .several  minutes  after  the  excitation  has 
ceasetl.  It  ha.s  been  found  that  pressure  brought  to  bear  U|M>n 
the  human  heart  where  a  defect  in  the  chest-wall  makes  it  acces>i- 


118 


CIRCULATION. 


ble  can  be  felt  by  the  subject,  and  direct  stimulation  of  the  sur- 
face of  the  heart  in  animals  may  cause  movements  of  the  limbs. 


Vaaal  or      \ 
extra-canZ.  infiid.  centn 


Diagrammatic  view  of  the  nerves  influencing  the  action  of  the  heart.  The 
right  half  represents  the  course  of  the  inhibitory,  and  the  left  the  course  of  the 
accelerating  nerves  of  the  heart:  the  arrows  showing  the  direction  in  which 
impressions  are  conveyed.  The  ellipse  at  the  upper  extremity  of  the  vagus  looking 
like  the  section  of  the  nerve  is  intended  to  represent  the  vagal  nucleus  or  centre. 
In  this  diagram  the  nerves  are  incorrectlv  made  to  cross,  instead  of  passing  behind, 
the  aorta  (Chapman). 


The  latter  event  is  absent  when  the  vagi  are  cut,  so  that  it  is 
thought  the  vagus  carries  afferent  fibred  to  the  brain,     Stimulation 


Tiih:  iiF.Ain:  I  r.i 

of  the  oontnil  end  t)i"  tlu-  cut  vaji:us  when  the  other  is  intact  slows 
the  licarl-nilc.      This  cl led  disappears  when  hoth  vai^i  arc  cut. 

The  ilej)re!<iior  is  a  nerve  whose  til)res  |)ass  tVoni  the  lieart  to  the 
central  nervous  system.  StHion  and  stiniiilaftoii  oi  i\\Q  peripheral 
end  cause  no  a|)|)reciable  change.  Slimnlntion  of"  the  central  end 
causes  a  general  tall  of  bhK)d-pressure  to  one-half  or  one-third  its 
former  height,  and  lessens  also  the  pulse-rate.  Both  are  restored 
after  stimulation  ceases.  When  both  vagi  are  cut  there  is  a  fall 
of  blood-pressure  u[)on  stimulation  of  the  depressor,  but  no  change 
in  the  pulse-rate.  This  shows  that  the  impulses  from  the  de- 
pressor may  spread  to  the  cardio-inhibitory  centre  and  through  the 
vagi  slow  the  heart.  It  shows,  moreover,  that  the  fall  in  pressure 
is  not  dependent  upon  the  vagi.  Section  of  the  Kjdunciudc  nerrc 
causes  dilatation  of  the  abdominal  vessels  and  a  fall  of  the  general 
blood-pressure.  If,  now,  the  depressor  is  stimulated,  no  effect  is 
produced,  because  the  blooil-pressure  is  already  so  low  that  little 
more  fall  can  be  brought  about.  If,  however,  the  general  press- 
ure is  raised  by  stimulation  of  the  splanchnic  or  by  the  injection 
of  saline  solution,  then  stimulation  of  the  depressor  produces  a 
typical  fall.  This  nerve  is  normally  made  active  by  stimuli  aris- 
ing from  the  endocardiuTn  of  the  heart  when  that  organ  is  over- 
charged with  blood.  The  impulses  are  conveyed  to  the  vaso- 
motor centre,  which  causes  a  dilatation  of  the  arterioles  all  over 
the  body.      Fnlike  the  vagi,  the  depressor  is  active  only  at  times. 

In  general  it  may  be  said  that  weak  stimulation  of  anv  .•<enmni 
)ierve  like  the  sciatic  produces  augmentor  effects,  while  a  strong 
stimulation  produces  inhibitory  effects.  Stimulation  of  the  central 
end  of  the  abdominal  sympathetic  produces  through  the  vagi  a 
reflex  inhibition  of  the  heart.  Di/afafion  of  the  .itomach  has  ex- 
perimentally been  shown  to  inhibit  the  heart. 

The  cardio-inhibiforji  centre  is  situated  in  the  bulb  at  the  level 
of  a  mass  of  cells  known  as  the  accessory  nucleus  of  the  twelfth 
and  the  nuclei  of  origin  of  the  ninth,  tenth,  and  eleventh  nerves. 
The  centre  is  probably  always  in  action,  since  section  of  the  vagi, 
which  removes  the  influence  of  the  centre,  is  followed  by  an  in- 
crease in  the  rate  of  the  heart-beat.  The  continuous  activity  of 
the  centre  is  due  to  a  stream  of  impulses  that  come  from  all  jior- 
tions  of  the  body.  After  cutting  off  most  of  these  by  dividing  the 
spinal  cord  near  the  bulb,  section  of  the  vagi  no  longer  increases 
the  heart-rate.     The  mtqmrntor  centre  is  situated  somewhere  in  the 


120  CIRCULATION. 

bulb  and  is  also  continuously  active.  This  is  shown  by  sectioning 
the  vagi  and  then  extirpating  the  inferior  cervical  and  first 
thoracic  ganglia  on  both  sides,  which  causes  a  slowing  of  the 
heart.  Dividing  the  cord  in  the  cervical  region  after  the  vagi 
have  been  cut  has  the  same  effect.  Inhibition  of  the  heart 
through  the  vagi  is  more  ea.^ily  obtained  when  the  augmentor  fibres 
have  been  severed.  Whenever  sensory  nerves  are  stimulated, 
producing  an  accelerated  heart-beat,  it  is  i)robable  that  both  the 
augmentors  and  the  cardio-inhibitory  centres  are  stimulated,  but 
the  first  more  strongly,  so  that  its  effects  prevail.  There  are  a 
few  cases  on  record  where  the  heart-centres  in  the  medulla  were 
apparently  influenced  by  impulses  from  the  cerebral  cortex,  but 
these  are  extremely  unusual. 

The  heart  of  the  higher  animals  has  a  distinct  arterial  and 
venous  system,  upon  which  its  nourishment  depends.  The  arteries 
in  the  human  heart  each  supply  a  given  area  of  the  muscle,  not 
invading  the  area  of  its  neighbors,  and  no  collateral  circulation  can 
be  established  between  them.  If,  therefore,  an  artery  is  plugged  by 
embolism  or  thrombosis,  the  part  of  the  heart-wall  that  it  supplies 
dies,  becoming  dull-white  or  faintly  yellow  in  color,  granular  in 
cross-section,  and  is  soon  replaced  l3y  connective  tissue.  Such  an 
area  is  known  as  an  infarct.  The  result  of  closure  of  the  arteries 
of  the  heart  depends  upon  the  size  of  the  vessel  operated  upon. 
Sometimes  no  effect  is  produced,  or  the  ventricles  may  stop  beating 
and  fall  into  fluttering,  twitching  movements  known  as  fibrillary 
contractions.  The  auricles  will,  perhaps,  continue  beating  for  a 
short  time.  As  the  arrest  of  the  heart  draws  near  the  force  of  the 
ventricular  beat  becomes  irregular,  but  the  pressure  in  the  heart 
gradually  lessens  during  systole  and  becomes  greater  during  dias- 
tole. The  cause  of  the  arrest  is  not  the  mechanical  injury  done  to 
the  heart,  but  to  the  sudden  anaemia  produced.  Anaemia  brought 
about  by  hemorrhage  produces  a  different  series  of  symptoms  be- 
cause the  heart  works  against  decreasing  resistance  in  the  arteries, 
which  is  not  the  case  when  a  branch  of  the  coronary  artery  is 
ligated,  for  then  the  peripheral  resistance  continues  to  be  high. 
Closure  of  the  coronary  veins  produces  fibrillary  contractions  in  a 
rabbit  in  from  fifteen  to  twenty  minutes,  but  is  without  effect  upon 
the  dog,  owing  to  the  fact  that  some  of  the  blood  passes  into  the 
cavities  of  the  heart  through  the  vence  Thebesii,  and  is  sufficient  in 
amount  to  maintain  the  nutrition  of  the  heart, 


MITKRJKS,    (WrriJ.APJKS  AXh    Vh'lXS.  iJl 

The  contractions  of  tlie  lu-iirt  favor  the  eiitraiici!  ol"  the  lAnoil 
into  the  coronary  arteries  in  two  ways  : 

1.  liy  the  pressure  protluced  in  the  aorta. 

2.  By  tlirectly  compressing  the  walls  of  the  hloijtlvesseis  in  tlie 
heart  muscle. 

It  has  heen  found  that  the  volume  of  the  hlooJ  passing  thrcnigh 
tlie  coronarv  circulation,  unless  it  varies  very  much,  does  not 
influence  tlie  rate  of  the  beat,  l>ul  does  modify  the  force  of  the 
contraction. 

The  varioK.'i  condttuenU  of  the  complex  jiu id,  blood,  have  diffrrint 
rnlueft  in  maintaining  the  activity  of  the  heart.  Tliis  has  been 
investigateil  bv  the  use  of  nutrient  solutions  of  definitely  known 
comjtosition.  The  results  obtained  are  briefly  ad  follows  :  Nutrient 
fiiii<ls  for  the  heart  must  be  alkaline  in  reaction.  iSodiiun  carbonate 
is  the  alkali  generally  used.  It  has  no  specific  action,  but  neutral- 
izes the  carbon  dioxide  and  acids  formed  l)y  the  activity  of  the 
heart  muscle.  Sodium  chloride  must  be  present  of  a  strength 
isotonic  with  the  blood  of  the  animal.  Rome  calcium  salt  to  pre- 
vent the  diH'usion  of  calcium  out  of  the  musde-tibres  is  essential 
to  continued  contraction.^.  Calcium  salt-i  tend  to  produce  prolongeil 
tonic  contractions,  and  this  effect  is  neutralized  by  the  addition  of 
pota.'isium  saltx.  When  calcium  salts  are  removed  from  a  solution 
l>y  the  addition  of  oxalate  compounds,  the  heart  cea.ses  to  beat,  but 
spontaneous  contractions  return  when  calcium  is  again  added.  A 
well-known  nutrient  solution  is  Ringer  .<,  which  is  a  mixture  of 
1(10  c.c.  of  a  0.(>  per  cent,  sodium  chloride  solution  saturated  with 
tribasic  calcium  phosphate  and  2  e.c.  of  a  1  per  cent,  solution  of 
potassium  chloride.  O.njijen  is  essential  to  the  ])rolonged  activity 
i)f  the  heart.  Carbon  dioxide  is  injurious  when  present  in  large 
ipiantities.  A  heart  poisoned  with  the  latter  substance  shows  an 
irregular  aeries  of  eoidi'actions.  It  has  not  heen  isatisfactorily  de- 
monstrated that  organic  substances  are  immediately  necessary  to 
{\\v  rhythmic  activity  of  the  heart. 

ARTERIES,  CAPILLARIES  AND  VEINS. 

The  continuously  high  /)rr.'<sure  that  exists  in  the  aorta  causes 
the  blood  to  move  to  points  (if  lower  pressure,  and  it  is  thus  kept 
in  constant  movement  from  tlic  arteries  through  the  capillaries  to 
the  veins,  and  .«o  hack  to  tin-  heart,  where,  bv  the  action   of  this 


122  CIRCULATION. 

organ  it  is  agaiu  transferred  into  the  artery  and  put  under  high 
pressure.  Blood-pressure  is  usually  measured  by  an  instrument 
called  a  mercurial  manometer.  It  consists  of  a  U-shaped  glass 
tube,  the  bend  of  which  is  filled  with  mercury.  One  limb  of  the 
tube,  filled  with  an  anti-coagulation  fluid,  is  put  in  connection  with 
the  bloodvessel  of  the  animal,  while  the  surface  of  the  mercury  in 
the  other  limb  carries  a  small  float  to  which  is  attached  a  delicate 
pen  that  bears  against  a  horizontally  moving  surface.  Such  an 
arrangement  is  a  kymograph.  Variations  of  the  blood-pressure 
within  the  vessel  are  transmitted  through  the  fluids  to  the  mercury, 
which  moves  up  and  down,  carrying  the  float  and  pen  with  it,  and 
are  thus  recorded.  By  this  method  it  is  found  that  the  blood  in  an 
artery  exhibits  at  least  two  regularly  recurring  changes  of  pres- 
surej  which  take  the  form  of  smaller  waves  superimposed  upon 

Fig.  16. 


Tracing  of  arterial  pressure  with  a  mercury  manometer  (Foster).  The  smaller 
curves,  p  p,  are  the  pulse-curves.  The  space  from  r  to  r  embraces  a  respiratory  undu- 
lation. The  tracing  is  taken  from  a  dog,  and  the  irregularities  visible  in  it  are 
those  frequently  met  with  in  this  animal. 


larger  ones.  The  latter  are  due  to  respiratory  movements,  while 
the  former  are  due  to  heart-beats.  The  mean  blood-pressure  is  the 
average  pressure  during  any  arbitrarily  chosen  length  of  time. 
This  in  man  is  about  200  mm.  of  mercury  fHg.)  or  more  in  the 
aorta  ;  from  30  to  50  mm.  Hg.  in  the  capillaries  ;  about  20  mm. 
of  Hg.  In  the  external  jugular  and  in  the  vei7is  near  the  Ixeart 
the  pressvre  becomes  negative.  From  the  aorta  through  the  capil- 
laries and  veins  back  to  the  heart  there  is  a  continuous  decline 
in  pressure. 

The  cajise  of  the  high  pressiire  in  the  aorta  is  the  intermittent 
entrance  into  it  of  jets  of  blood,  the  resistance  offered  by  the 
peripheral  capillaries  and  the  elasticity  of  the  vessel-walls.  Each 
volume  of  blood  forced  into  the  aorta  from  the  heart  extends  the 


ARTl-.niES,    CM'll.l.MllF.X   ,l.\7>    VFISS.  1 L'.'} 

wall  of  the  vessel,  which,  through  its  elasticity,  tends  gradually 
to  return  to  its  normal  size  during  every  diastole  of  the  heart. 
It  is  at  all  times,  however,  stretched,  and  therefore  always  exerts 
a  pressure  upon  tiu'  blood  within.  Under  normal  condition.s  the 
amount  of  lilood  accommodated  l)y  the  yielding  artery  during 
each  systole  is  eipial  to  the  amount  that  passes  from  the  arteries 
and  to  the  capillaries  during  tiie  diastole  of  the  heart.  Each  in- 
crease of  pressure'  caused  by  the  heart-beat  is  propagated  in  the 
form  of  a  wave  through  the  arterial  system,  and  constitutes  what 
is  called  the  jiulxr. 

The  pressure  in  the  capillaries  and  veins  is  caused  by  the  same 
factors  that  are  present  in  the  aorta — power  of  the /(rar<,  reaixtance 
oi' friction,  and  c/nxtirifij  of  hlDodvexsrl-ivall'^.  But  in  the  cajnlla- 
rirs  and  rciii.s  their  is  no  jmlxr  and  the  jjirxfutre  is  lotr.  The  cau.se 
of  the  latter  becomes  obvious  when  it  is  taken  into  consideration 
that  a  part  of  the  force  of  the  heart  has  l)een  lost  in  overcoming 
the  friction  of  the  bloodve.-^sels.  In  addition,  the  friction  which 
the  blood  has  yet  to  overcome  in  its  passage  back  to  the  heart  is 
but  a  fraction  of  the  total  friction  which  it  encountered  at  first. 
Diminished  resistance  ahead  means  lowered  pressure.  The  blood 
in  the  capillaries  has  become  pulseless,  because  the  elasticity  of 
the  arteries  displaces  the  blood  in  the  capillaries  at  the  same  rate 
that  the  systole  of  the  heart  does. 

There  are  siihxirJiani  forces  that  assist  the  heart  in  propelling 
the  blood.  Among  these  may  be  mentioned  the  coniractionx  of 
the  skelefnl  miixclex,  the  constant  jmll  of  the  Jibrcx  of  the  lumj,  and 
the  movemenU  of  rexpirafion.  The  muscles,  in  contracting,  press 
upon  the  veins  moving  the  contained  blood  onward,  since  the 
valve?  prevent  all  back-flow.  The  fibres  of  the  lungs,  through 
their  elasticity,  are  constantly  pulling  upon  the  walls  of  the  heart 
and  the  large  veins,  which  "tends  to  draw  the  blood  into  them. 
This  effect  is  increased  with  each  inspiration,  and  the  blood  then 
rushes  in  at  a  (juickcr  rate  ;  during  the  following  exjnration  the 
blood  flows  more  slowly  again.  There  may  in  this  way  arise  a 
diMinct  pvhe  in  the  large  revovs  vexHels  of  the  ched,  which  may 
extend  along  the  rcivx  to  the  root  of  the  vrck.  In  this  region,  in 
deep  respirations,  there  may  be  an  intermittent  flow  of  blood  from 
a  cut  vein.  The  Ideeding  occurs  during  each  expiration  and 
ceases  during  each  inspiration,  when  the  blood  is  sucked  past  the 
Wounil  and    not  jircssed  out  of  it.      Owing  to  this   reason  air  may 


124 


CIRCULATION. 


be  drawn  into  the  vein,  an  event  which  causes  immediate 
This  region  is,  therefore,  known  as  the  dangerous  region. 


death. 


Trace  of  the  radial  pulse  taken  by  the  sphygmograph  (Daltoii). 

By  the  term  arterial  pulse  is  meant  the  fluctuations  of  arterial 
pressure  that  correspond  to  the  beats  of  the  heart.  The  pulse  is 
dependent  upon  : 

1.  The  contractions  of  the  heart. 

2.  Upon  the  resistance  produced  by  the  friction  of  the  blood  in 
the  vessels, 

o.  Upon  the  elasticity  of  the  bloodvessel-walls.  An  abnormal 
change  in  either  of  the  three  will  modify  its  character.  An  artery 
not  only  increases  in  its  girth  as  the  pulse-wave  sweeps  over  it, 
but  also  in  its  length,  which  can  readily  be  seen  when  the  vessel 
has  a  sinuous  course.  The  increase  in  girth  can  be  felt  with  the 
finger,  and  forms  a  constant  means  of  diagnosis.  The  rate  of  the 
pulse-wave  is  from  3  to  9  metres  a  second.  As  the  blood  moves 
on  an  average  in  the  arteries  only  a  half  metre  in  the  same  time, 
it  is  clear  that  it  is  not  the  travelling  of  the  blood  that  produces 

Fig.  18. 


Dicrotic  pulse  of  typhoid  fever  (Marey). 

the  pulse,  but  a  wave  of  pressure.     A  number  of  terms  describe 
the  character  of  the  pulse.     In  regard  to  its  tension  it  may  be  : 

Of  high  tension  or  of  low  tension. 

Incompressible  or  compressible. 

Hard  or  soft. 

Very  hard  (wiry^  or  very  soft  Tgaseous). 

JSigh  tension  is  indicative  of  high  blood-pressure,  and  can  be 


AriTi:nir:s,  capiilmiiks  .ixn  veins. 


12;', 


liU'iisiin'd  1)V  a  s|ili\  ir'iiiiiiutcr.  In  iciranl  In  its  sizr  the  pulse 
niiiy  1)0  : 

Larj^c  or  small. 

Very  larj^e  (l)oun(lin<ij;  or  very  small  ( thready). 

A  lar<,fe  pulse  often  indicates  a  low  mean  l)loo<i-pressure.  Finally, 
the  pulse  may  be  short  or  lon;^.  It  is  long  when  the  upstroke 
takes  place  slowly. 

While  an  experienced  physician  can  aj)preciate  slij,Mit  variations 
iu  the  character  of  the  pulse,  it  is  only  by  means  of  the  irraphic 
method  that  diti'ercnt  kinds  of  pulse  can  be  investigated  success- 
fully and  records  kept.  The  .y)hj/(j)no(/ruj)k  is  an  instrument 
which  measures  the  succession  of  alternate  dilatations  and  c(ni- 
tractious  of  an  artery,  magnifying  the;u,  and  registering  them  on 

Fio.  19. 


Miirey's  spliyRmograph  applied  to  the  arm  (Marey). 


a  surface  moving  at  a  uniform  rate  by  clockwork.  The  tracings 
show  variations  of  the  pulse  too  slight  to  be  appreciated  by  the 
most  experienced  fingers.  The  record  of  a  sphygmograph  is  called 
a  ftplnif/mnfjram.  Each  pulsation  of  the  artery  is  seen  to  be  made 
up  of  a  sudden  and  direct  upstroke  and  a  gradual  oscillating  down- 
stroke.  The  latter  in  typical  tracings  is  made  up  of  three  waves, 
of  which  the  middle  one  is  the  most  pronounced,  and  is  known  as 
the  dicrotic  ware.  When  the  dicrotic  wave  can  be  felt  with  the 
finger,  the  pulse  is  spoken  of  as  a  dicroHc  pit/.-^e.  This  is  apt  to 
nccompami  a  low  bfoivl-prr.'i.oiire.  The  dicrotic  ivare  i'^  cau.'<cd  l>>j  the 
.tudilrn  chh'fure  of  the  ■'<emi!tniar  vn/vcs. 

The  blood  moves  through  the  arteries  in  a  series  of  pulses  which 
grow  less  and  less  pronounced,  until  they  are  extinguished  in  the 
capillary  district.     Here  the  blood  flows  toward  the  veins  with 


126 


CIRCULATION. 


much  friction,  slowly  and  under  comparatively  low  pressure. 
Instruments  have  been  devised  to  measure  rapid  fluctuations  of 
speed.  They  consist  essentially  of  a  needle,  which  is  thrust  through 
the  wall  of  the  vessel.  The  amount  that  it  is  deflected  from  the 
perpendicular  by  the  movement  of  the  blood  is  read  on  a  graduated 
semicircle  which  is  placed  under  the  free  end  of  the  needle.  It 
has  been  ascertained  that  the  blood  in  the  large  arteries  flows  at 
a  rate  of  from  250  to  over  500  mm.  a  second.  The  speed  in  the 
veins  is  somewhat  slower.  In  the  capillaries  it  has  been  measured 
directly  under  the  microscope,  and  some  physiologists  have  observed 
it  in  the  retinal  capillaries  of  their  own  eyes.     It  flows  from  0.6  to 


--0 


1    23  4 


1234 


Tracings  of  variations  of  rapidity  and  of  pressure  of  blood  in  the  carotid  of  a 
horse,  obtained  by  f'hauveau  and  Lortet.  Tlie  line  v  represents  the  curve  of  the 
rapidity  of  the  blood ;  and  p  the  curve  of  arterial  pressure.  The  figures  and  verti- 
cal lines  represent  corresponding  periods  in  the  tracings  (McKendrick) 

0.9  mm.  a  second.  The  speed  and  pressure  of  the  blood  rise  and 
fall  together  in  the  arteries,  but  whereas  the  pressure  falls  contm- 
uously'from  arteries  to  veins,  the  speed  falls  from  arteries  to  capil- 
laries, but  is  increased  again  as  it  approaches  the  heart.  The  speed 
does  not  depend  upon  the  pressure  alone,  but  also  upon  the  width 
of  the  blood-path.  Whenever  a  vessel  divides,  the  cross-sectional 
area  of  its  branches  is  greater  than  that  of  the  vessel  itself 
The  collective  sectional  area  of  the  capillaries  is  several  hundred 
times  that  of  the  aorta,  while  the  latter  is  half  that  of  the  vense 
cavse.     The  blood  then  flows  swiftly  through  the  arteries  to  the 


AtlTKniKS,   CM'ILI.MIIES  AM)    I'/.V.V.S'.  1 -JT 

(•:i|)ilhiries,  whore  it  perlornis  its  functions  and  is  returned  iiliuusl 
as  (juieklv  to  ilie  heart  hy  tlie  veins.  It  has  been  estimated  that 
the  hh)od  remains  ai)oul  (>.(•  of  a  second  in  a  (a|iillary  •]  mni. 
Ions:. 

The  pulmonary  circulation  ilitiers  in  minor  res|)ects  from  the 
siisfi-itiir.  The  total  j'rirlioii  is  Icsh,  m  correspondence  with  wliicli 
the  riijht  ventricular  walls  are  far  thinner  than  those  of  the  left 
ventricle.  Owinj;  to  the  fact  that  the  pnlmoimry  .■<ydein  lies  en- 
tirely within  the  thorax,  it  is  xithjcrted  to  the  luyndre  prcxxure 
which  exists  there,  and  the  veins  and  arteries  are  opened  hy  the 
elastic  pull  of  the  lunsrs  This  tends  to  favor  the  How  m  the  veins 
and  to  hinder  it  in  the  arteries  The  How  in  the  latter,  however, 
is  not  affected  much  on  account  of  the  thickness  of  the  arterial 
walls,  so  that,  on  the  whole,  the  negative  pressure  in  the  thorax, 
increased  with  each  iiispiratin)i,  helps  the  jxdmonary  circulatioti. 
The  capillaries  are  situated  so  close  to  the  surface  that  they  are 
exposed  to  atmospheric  pressure.  Every  expiration  presses  the 
blood  out  of  them,  and  so  aeain  the  tlow  is  favoreil. 

The  heart  pionp.-i  the  blond  thmiK/h  all  part. •<  of  the  body,  but  the 
amount  in  any  one  portion  depend.'^  upon  the  active  dilatation  or 
contraction  of  the  vesseL'i.  That  an  artery  may  dilate  was  first 
shown  by  Bernard,  who  cut  the  cervical  .'sympathetic  of  a  rabbit  on 
one  side  and  found  an  increased  redness  of  the  skin  of  the  ear  and 
an  elevation  of  the  temperature  of  from  four  to  six  deffrees.  which 
persisted  for  months.  If  the  peripheral  end  of  the  cut  nerve  is 
.stimulated  with  a  ijalvanic  current,  normal  conditions  are  resumed, 
and  which  last  oidy  as  lonj;  as  the  stimulus  is  applied.  The  existence 
of  dilator  nerve's  is  jilaced  beyond  doubt  bv  the  results  obtained 
upon  the  chorda  tympani  of  the  submaxillary  irland.  Nerves  that 
bring  about  a  dilatation  of  bloodvessels  are  called  vasodilator 
iicrves  ;  those  that  cause  a  constriction  are  called  va.'socom^trictor 
nerve's.  Both  are  present  in  the  nerves  of  the  sympathetic  system, 
as  well  a.s  i)i  the  cerebro.tpinal  and  .•<])inal  )ierves.  They  also  supph/ 
veins.  The  portal  vein,  for  instance,  may  be  made  to  contract  by 
stimulation  of  the  peripheral  end  of  the  cut  splanchnic.  The 
chanires  in  the  cai)acity  of  the  bloodves.sels  may  be  studied  by 
direct  inspection  in  many  ca.ses.  but  oflen  it  is  more  sati.^factory  to 
place  a  manometer  in  a  branch  of  the  artery  that  supplies  the  por- 
tion of  the  animal  under  observation.  The  principle  underlvinc: 
this  is  that  the  pressure  in  an  artery  depends  upon  the  resistance 


128  CIRCULATION. 

to  be  overcome  in  its  distal  capillaries.  Another  method  of  study- 
ing vasomotor  phenomena  is  to  inclose  a  portion  within  an  air-tight 
cylinder,  which  usually  is  filled  with  a  liquid  and  is  connected  with 
a  tambour.  Changes  in  volume  of  the  parts  inclosed,  due  to  vari- 
ations in  the  amounts  of  blood,  are  transmitted  to  a  tambour.  Such 
an  instrument  is  called  a  plethysmograph. 

Vasoeo)istrictor  and  vasodilator  nerves  are  usually  found  in  the 
same  nerve-trunk.  Upon  stimulation  the  effects  of  one  may  be 
entirely  masked  by  the  eff'ects  of  the  other,  so  that  it  becomes 
necessary  to  learn  the  differences  between  the  two. 

1.,  The  vasoconstrictors  are  excited  less  easily  than  the  vasodi- 
lators, 

2.  The  after-effect  of  stimulation  of  the  constrictors  is  shorter 
than  that  of  the  dilators. 

3.  Warming  increases  the  excitability,  and  cooling  decreases  it, 
more  in  the  constrictors  than  in  the  dilators. 

4.  The  maximum  effect  of  stimulation  is  reached  more  quickly 
in  the  constrictors  than  in  the  dilators. 

5.  The  constrictors  have  a  latent  period  of  1.5  seconds ;  that  of 
the  dilators  is  3.5  seconds. 

There  is  in  the  medulla  in  the  anterior  part  of  the  lateral  col- 
umns on  each  side  of  the  median  line  a  group  of  cells  known  as 
the  anterolateral  nucleus  of  Clarke.  This  is  the  situation  of  the 
vasomotor  centre.  It  is  bilateral,  and  occupies  an  area  caudal  to 
the  corpora  quadrigemina.  When  sections  are  made  through  suc- 
cessive levels  of  the  bulb,  the  pressure  of  the  blood  begins  to  fall 
when  a  point  is  reached  about  1  mm.  caudal  to  the  quadrigemina, 
and  continues  to  fall  until  an  area  extending  over  the  fourth  mil- 
limetre has  been  reached.  There  is  then  no  further  fall.  The 
centre  continually  sends  impulses  along  fibres  that  extend  to  the 
nuclei  of  various  cranial  nerves,  and  also  down  the  lateral  columns 
of  the  cord  to  small  cells  situated  at  various  levels  in  the  anterior 
horn  and  lateral  gray  substances.  From  these  cells  axis-cylinders 
pass  out  through  the  anterior  roots  of  the  cranial  and  spinal  nerves 
and  enter  the  sympathetic  ganglia.  Here  cells  in  turn  send  out 
processes  that  end  on  the  muscle-fibres  of  the  bloodvessels.  The 
evidence  for  the  existence  of  .subsidiary  .spinal  centres  is  conclusive 
It  has  been  found  that  m  a  dog  whose  cord  is  severed  at  the  junc- 
tion of  the  dorsal  and  lumbar  regions  mechanical  stimulation  of 
the  skin  of  the  abdomen  and  penis  will  cause  erections.     This  is  a 


ARTERIES,   CA riL LAR TF.S 

vasomotor  reflex  due  to  dihitatioii  of 
l)loodvessels  of  the  penis  through  the 
nervi  erigeiitca.  Again,  section  of  the 
cord  in  the  dorsal  region  of  a  dog  is 
followed  by  a  vasodilatation  of  the  ar- 
teries of  the  hind  limbs.  If  the  animal 
continues  to  live,  the  limbs  are  in  time 
restored  to  their  normal  comlition.  De- 
struction of  the  luMd)ar  cord  now  brings 
on  a  second  dilatation.  It  must  be  a.><- 
sumed,  therefore,  that  centres  exist  in 
the  cord  which  normally  are  control lc<l 
by  the  bulbar  centre,  and  that  when  sev- 
ered from  the  latter  will  become  grad- 
ually independent.  There  are,  m  ad- 
dition to  the  vasomotor  centres  already 
mentioned,  centrca  in  the  KijinjMtfliefic 
(juuijUa.  DedrucHon  of  both  hit/bar 
and  spina/  centre'^  does  not  destroii  ar- 
terial tone  completehj.  For  exami)le, 
the  lower  portion  of  the  spinal  cord  of 
a  dog  was  removed  for  about  80  mm. 
The  dilatation  of  the  vessels  of  the  hind 
limbs  which  followed  was  succeeded  in 
time  by  a  constriction,  leaving  the  tem- 
jierature  of  the  limbs  even  cooler  than 
normally 

IjOng  oscillation.^  in  blood-pressure 
curves  due  to  vasomotor  changes  are 
called  Travbe-Herinrj  waves.  They  //'- 
dicate  alterations  in  the  tonnx  of  the 
bloodvessels,  and  are  cau-^ed  by  irradi- 
ations of  impulses  from  other  centres 
to  the  vasomotor  centre.  Va.<iomotor 
reflexes  arise  bv  impulses  which  come 
either  from  the  bloodvessels  or  from 
the  end-organs  of  sensory  nerves.  In 
the  latter  case  the  dilatation  affects  not 
only  the  portion  from  which  the  im- 
pulses come,  but  also  parts  functionally 

9-PhTS. 


Diapram  illustrating  the 
paths  of  vusoconstrictiir  fibres 
alon^'thecervu'ul  sympathetic 
and  tj)art  oil  the  abdominal 
splanchnic  (Foster):  .Iwc,  ar- 
tiTV  (if  ear;  G.C.S.,  superior 
eorVical  gan-jlion ;  .1/"^  Spl., 
upper  roois  of  and  part  of  ab- 
dominal splanchnic  nerve; 
V  M  ('.,  vasomotor  centre  in 
medulla;  ('  Sy.  cervical  sym- 
ivathetic-  O.  '',  lower  cervical 
panslinn;  O.  771. '  to  G.  Th.-. 
the  thoracic  panplia,  first  to 
seventh  both  inclusive:  P.  II- 
and  7>  V.  respectively  the 
second  and  (ifth  dorsal  nerve  : 
Av.  V.  anntdus  of  Vieussens. 
The  patlis  of  the  constrictor 
fibres  are  shown  by  tbcarrows 
The  dotted  line  in  Itie  spinal 
cord,  S'p.  ('.,  is  to  indicate  the 
passage  of  constrictor  impulses 
down  the  conl  fr^m  the  vaso- 
motor centre  in  the  medulla. 


130  CIRCULATION. 

related.  Thus  stimulation  of  the  tongue  causes  dilatation  of  the 
vessels  of  the  submaxillary  gland.  There  is  no  sufficient  evidence 
of  the  existence  of  vasomotor  centres  in  any  portion  of  the  brain 
except  the  bulb.  The  fact  that  stimulation  of  the  same  nerve 
gives  rise  sometimes  to  a  reflex  dilatation  instead  of  the  more 
usual  constriction,  has  given  rise  to  the  conception  of  special  pres- 
sor and  depressor  fibres.  The  former  constrict,  the  latter  dilate. 
The  cardiac  depressor  nerve  is  a  good  example. 

CIRCULATION  OF  LYMPH, 

The  lymph,  in  moving  from  the  tissue-gaps  and  lymph-capil- 
laries to  the  veins,  passes  from  a  point  of  relatively  high  pressure  to 
one  of  low  pressure.  The  pressure  in  the  lymph-capillaries  has 
been  estimated  at  from  12  to  25  ram.  of  Hg.  ;  in  the  thoracic  duct, 
near  its  entrance  into  the  veins,  it  is  very  near  to  zero,  and  often  is 
negative.  In  some  of  the  lower  animals  there  are  separate  lymph- 
hearts  which  act  as  force-pumps  to  drive  the  lymph  on.  In  man 
such  lymph-hearts  do  not  exist,  but  the  movement  is  brought  about 
by  other  factors : 

1.  By  the  continual  formation  of  new  lymph. 

2.  By  the  muscular  movements  of  the  body  compressing  the 
lymphatics,  which  force  the  lymph  on  in  the  proper  direction,  the 
reverse  flow  being  prevented  by  valves.  The  chyle  is  aided  in  its 
flow  by  the  action  of  the  muscular  fibres  of  the  small  intestine  and 
also  by  the  contractions  of  the  villi.  In  the  mouse  the  chyle  has 
been  seen  to  flow  with  the  intermittent  movements  corresponding 
to  the  peristaltic  waves.  The  contractility  of  the  ivalls  of  the 
lymph-vessels  themselves  probably  aid  the  flow. 

3.  The  thoracic  aspiration  of  the  chest  on  inspiration  draws  the 
lymph  into  the  thoracic  cavity  in  the  same  manner  as  it  draws  the 
venous  blood.  The  movement  of  the  lymph  is,  without  doubt, 
irregular,  but  in  the  course  of  a  day  a  considerable  amount  is 
poured  into  the  veins.  An  accumulation  of  lymph  in  the  gaps  of 
the  tissues  constitutes  dropsy,  and  such  tissue  is  said  to  be  ocdemor 
tous.  A  substance  in  solution  injected  into  the  blood  can  be  de- 
tected at  the  mouth  of  the  thoracic  duct  in  from  four  to  seven 
minutes. 


QUESTIONS  OX  CIIAPTFJi    Mil.  131 


QUESTIONS  ON  CUAPTEK  VIII. 

Give  the  path  of  the  I»1(«mI  throuuli  thi-  body. 

Givi-  the  putli  of  thi-  hliuKi  lliniu;ih  tho  jioital  systfUi. 

Wluil  is  iiicaiil  l)y  ■' ciii-iilation  uf  ilir  hlood"'? 

What  I'liiiiiiun  is  I'lillilKd  l>y  the  ciiriilatiuii  ? 

Wlii-nci-  iliM.',s  the  lioarl  ilerivc  il.s  uMt-rgy  ? 

Dcliiie  systole  and  diastule. 

By  wliat  meaus  is  tlie  hUnid  forced  in  one  direction  only? 

How  nnuh  time  is  retiuiied  by  the  hlood  to  eoniplete  its  eireiiitV 

What  dilferent  events  take  place  during  a  cardiac  cycle? 

What  are  the  changes  in  the  size  of  the  heart  due  to? 

What  is  the  contlition  of  the  heart  when  relaxed  ? 

What  changes  take  place  in  the  heart  during  systole  when  the  thorax  is 
open? 

How  are  these  changes  luoditied  in  the  unopened  chest? 

Give  the  changes  of  color  of  the  heart  during  contraction. 

Why  does  the  heart  not  move  from  the  chest-wall  during  sj'stole? 

Where  is  the  apex-beat  felt? 

What  is  meant  by  "negative  impulse"? 

Describe  the  sounds  of  the  heart. 

With  what  portions  of  the  cardiac  cycle  do  they  coincide? 

What  is  the  cause  of  the  heart-.sounds? 

Where  can  the  sounds  be  best  heard? 

Discuss  the  rate  of  the  heart-heat. 

Describe  the  character  of  the  contractions  of  the  auricle  and  ventricle. 

Give  the  times  involved  by  the  various  events  of  the  cardiac  cycle. 

What  changes  take  place  in  regard  to  the  time  occupied  by  the  cardiac  cycle 
events  when  the  heart-rate  is  quickened? 

Describe  the  action  of  the  valves  during  a  heart-beat. 

What  is  the  pulse-volume? 

How  is  the  iiulso- volume  obtained?     What  is  its  value? 

How  is  the  work  of  the  heart  calculati'd  ? 

How  are  intraventricular  ])ressures  determined? 

How  much  work  does  the  heart  do  in  a  day? 

What  are  the  relative  jiressures  in  ventricle  and  aorta? 

Discuss  endocardiac  pressure  curves  obtained  from  ventricle  with  different 
methods. 

What  are  the  oscillations  of  tho  plateau  due  to? 

In  what  way  may  the  times  of  closure  and  opening  of  the  valves  be  ascer- 
tained on  intracardi;ic  jire.ssure-cnrves? 

Define  "period  of  reception"  and  "period  of  ejection." 

Discn.ss  periods  of  complete  closure  of  the  ventricles. 

fan  the  ventricles  alone  niaintain  circulation? 

What  is  the  function  of  the  auricles? 

What  variations  in  pressure  arc  there  in  the  auricles? 

DiscMiss  the  entrance  of  the  blood  into  the  auricles  from  the  veins. 

Discuss  the  cause  of  the  rhythmic  activity  of  the  heart. 

What  is  the  "cardiac  excitation  wave"? 

Where  does  the  contnK'tioii  of  the  heart  begin? 

What  is  the  effect  of  tying  a  ligature  about  the  aiiriculoventriculargroove? 

What  is  the  speed  of  the  cardiac  excitation  wave? 

WTiat  is  the  latent  period  of  the  frog's  heart-muscle? 

What  is  the  time- value  of  the  block  of  the  heart's  contnu-tiou? 


132  CIRCULATION. 

What  is  the  cause  of  the  block  ?     Give  evidence. 

What  is  meant  by  the  refractory  period  of  the  heart^beat? 

Define  compensatory  pause. 

What  are  the  sources  of  the  nerve-fibres  to  the  heart?  Describe  their 
course. 

Discuss  the  effect  of  stimulation  of  the  vagus  on  the  heart-beat. 

How  does  stimulation  of  the  vagus  afl'ect  a  demarcation  current  from  the 
auricle  ? 

Discuss  the  end-apparatus  by  means  of  which  the  vagi  inhibit  the  heart. 

What  is  the  eflect  of  stimulation  of  the  augmentor  fibres  on  the  heart-beat  ? 

Give  the  lengths  of  the  latent  periods  of  inhibition  and  acceleration. 

What  evidence  that  afferent  fibres  run  from  the  heart  to  the  central  nervous 
system  ? 

Discuss  the  function  and  the  effects  of  stimulation  of  the  central  cut  end  of 
the  depressor  nerve. 

Are  the  vagi  and  depressor  nerves  continuously  active  ? 

How  do  weak  and  strong  stimulation  of  sensory  nerves  affect  the  heart? 

What  effect  has  dilatation  of  the  stomach  on  the  heart? 

Discuss  the  situation  and  action  of  the  cardio-inhibitory  centre. 

Discuss  the  action  of  the  accelerator  centre. 

Where  are  the  ligatures  of  Stannius  placed,  and  what  effect  do  they  pro- 
duce? 

What  is  the  peculiarity  in  the  distribution  of  bloodvessels  to  the  heart? 

What  is  an  infarct  ? 

How  does  the  antemia  resulting  from  hemorrhage  differ  in  its  action  from 
that  caused  by  ligating  the  coronary  artery  ? 

How  do  the  contractions  of  the  heart  favor  the  entrance  of  blood  into  the 
coronary  arteries? 

In  what  ways  does  the  blood-supply  to  the  heart  affect  its  beat? 

Discuss  the  constituents  of  the  blood  that  cause  the  rhythmic  activity  of  the 
heart. 

How  do  the  actions  of  potassium  and  calcium  salts  differ? 

What  is  Ringer's  solution  ? 

What  effect  has  carbon  dioxide  on  the  heart? 

Why  does  the  blood  move  from  the  arteries  to  the  veins  ? 

How  is  blood- pressure  measured  ? 

Describe  a  mercurial  manometer. 

What  is  the  form  of  blood- pressure  curves  obtained  from  an  artery? 

What  is  meant  by  mean  blood-pressure? 

What  are  the  mean  blood-pressures  in  arteries,  capillaries,  and  veins? 

What  is  the  cause  of  the  high  pressures  in  the  arteries? 

What  are  the  causes  of  blood -pressure  in  capillaries  and  veins? 

Why  does  the  pressure  decline  from  arteries  to  veins? 

Why  is  there  no  pulse  in  the  veins? 

Discuss  the  action  of  subsidiary  forces  that  aid  the  heart  in  circulation. 

What  is  the  pulse  ?    Its  cause  ? 

How  does  the  character  of  the  pulse  vary  ? 

What  is  a  spbygmogram? 

What  is  the  dicrotic  wave  ?    Its  cause  ? 

How  are  rapid  changes  in  the  velocity  of  the  blood  measured  ? 

Give  the  rate  of  flow  of  the  blood  and  the  causes  for  its  variations. 

How  long  does  the  blood  remain  in  the  capillaries  ? 

How  does  the  pulmonary  difl"er  from  the  systemic  circulation? 

What  governs  the  distribution  of  the  blood  in  the  body  ? 


JUCaVl  RATION.  133 

What  urc  vasomotor  libns?     (Jive  proofs  that  tliij'  exist. 

Are  vasomotor  lilircs  iircsont  in  Vfiiis? 

(live  tilt'  miaiis  ol'  (lisUiiKnisiiiiiK  lu-twifii  dilator  ami  constrictor  fibres. 

Discuss  IIk-  location  of  the  vasomotor  cent  re  and  its  commnnicatiuiis. 

What  is  till'  ovidcncf  that  siiinal  ami  symiiallu-lic  vasomotor  centres  exist? 

What  are  Tranhe-Ilerinj;  waves  and  their  cause? 

I  low  do  vasomotor  rellexes  arise? 

What  are  pressor  and  depressor  lihres? 

Discuss  the  factors  that  cause  tlic  llow  of  the  lymph. 

What  constitutes  ilropsy  ? 

What  is  the  rapidity  of  the  lymph  circulation? 


CHAPTER    IX. 

RESPIRATION. 

The  expression  resplrafiom\Xi\n'\xcQs  two  distinct  ideas.  It  may 
mean  the  entrance  of  oxi/gcn  into  and  the  exit  of  carbon  dioxide 
Iroin  an  animal,  or  it  may  have  reference  to  the  visceral — muscu- 
lar and  pulmonary,  etc. — movements  by  which  these  f/ases  are 
caused  to  fow  in  and  out  of  the  Innrj.^.  The  lungs  of  man  are  of 
vital  iin])ortance  in  the  interchange  of  oxygen  and  carbon  dioxide, 
while  the  tkin  is  of  but  .■inhxidianj  importance.  This  condition  of 
affairs  is  reversed  in  the  frog.  The  hmfjs  consist  of  an  enormous 
number  of  air-vesicles  or  alveoli  which  communicate  by  means  of 
a  series  of  passages  with  the  trachea  and  the  external  air.  Their 
total  area  is  more  than  one  hundred  times  the  superficial  area  of 
the  skin,  and  their  walls  form  a  delicate  partition  in  intimate  rela- 
tion to  the  blood^capillaries  of  the  htnci.  Before  birth  the  liin(is 
are  airle.^s  {atelectatic),  but  after  having  once  been  expanded, 
they  never  regain  their  atelectatic  condition,  becau.se  during  col- 
laji.-'c  the  pas.-^acjes  cloxc  fir.4  and  so  imprison  some  air  in  the 
alveoli.  The  Imigs  are  enclosed  in  the  air-tight  thorax,  and  sepa- 
rateil  from  its  walls  by  a  double  layer  of  jdeiira.  The  thora.r  of 
the  child  grows  faxter  than  the  hnujx,  so  that  the  latter  become 
didended  in  an  air-tight  cavity.  Whenever  the  thorax  is  o]iened, 
the  lungs,  owing  to  the  ela.dieiti/  of  their  structure,  immediately 
shrink  together.  It  follows,  therefore,  that  the  lungs  are  always 
tentling  to  shrink  and  thus  jniUing  away  from  the  thoracic  walls 
and  didplinirpn.  This  produces  a  prcx.'nire  in  the  pleural  cavity 
below  that  of  the  aimoaphere,  and  it  is  called  a  negative  pressure 


134  RESFIBA  TION. 

whenever  atmospheric  pressure  is  regarded  as  a  standard.  The 
negative  pressure  has  been  found  to  vary  greatly  under  different 
conditions,  but  may  be  put  at  minus  6  mm.  of  Hg  at  the  end  of 
a  quiet  expiration,  and  at  minus  9  mm.  of  Hg  at  the  end  of  a 
quiet  inspiration.  During  forced  inspiration  the  value  may  reach 
minus  40  mm.  of  Hg.  The  pressure  in  the  pleural  cavity — i.  e., 
outside  of  the  lungs  and  within  the  thorax — is  known  as  intra- 
thoracic pressure,  while  that  within  the  lungs  and  respiratory 
passages  is  called  the  intrapulmonary  pressure.  The  variations 
in  pressure  are  caused  by  changes  in  the  capacity  of  the  thorax, 
which  may  enlarge  in  all  directions.  It  is  obvious  that  when  the 
thorax  increases  in  size  the  decreased  pressure  within  causes  the 
entrance  of  air  from  the  outside,  where  it  is  at  a  higher  pressure. 
The  air  rushes  through  the  trachea  and  inflates  the  lungs.  This 
constitutes  an  insjnration.  The  opposite  process,  or  an  expulsion 
of  air  by  a  decrease  in  the  size  of  the  thorax,  is  expiration,  and 
both  together  form  respiration.  The  lungs  during  respiration  are 
entirely  passive,  and  merely  follow  the  thoracic  walls  because  the 
atmospheric  pressure  acting  on  their  inner  surfaces  is  greater  than 
that  between  the  lungs  and  the  thoracic  walls.  The  pleurae  are 
moistened  with  lymph,  and  slide  over  each  other  without  fric- 
tion. 

Inspiration  is  an  active  process  brought  about  by  certain  mus- 
cles which,  by  their  action,  enlarge  the  thorax  in  a  vertical, 
anteroposterior,  and  lateral  direction.  The  upper  part  of  the 
thoracic  cage  being  fixed,  the  vertical  diameter  is  increased  by 
the  descent  of  the  diaphragm  in  contracting.  Other  muscles  act 
on  the  ribs,  so  that  they  turn  on  their  axes,  with  the  result  that 
their  sternal  ends  are  raised  up  and  carried  forward,  enlarging 
the  anteroposterior  diameter;  at  the  same  time  the  direction  of  the 
axes  of  the  ribs  causes  them  to  rotate  outward  and  upward,  so  in- 
creasing the  lateral  diameter.  The  chief  muscles  of  inspiration  are 
the  diaphragm,  the  scaleni,  the  serrati  postici  superiores  et  infe- 
riores,  the  levatores  costarum  breves  et  longi,  and  the  external 
intercostals  and  interchondrals.  The  diaphragm  projects  into  the 
thoracic  cavity  in  the  form  of  a  flattened  dome.  During  contrac- 
tion it  descends  from  5.5  to  11.5  mm.  in  quiet  respiration,  and  about 
42  mm.  in  deep  inspiration.  There  is  a  tendency  for  the  dia- 
phragm to  pull  in  its  points  of  attachments — the  lower  ribs,  with 
their  cartilages,  and  the  lower  portion  of  the  sternum,  but  usually 


RESPIRA  TJ'jy.  135 

this  is  counterbalanced  by  the  pressure  of  the  abdominal  viscera. 
The  ."•errati  po.slici  iiit'eriore.<  assist  the  (liaphra;zni  by  fixing  the 
ninth,  teiitli,  eleventh,  and  twelfth  rii»s.  Tlie  sealeni  lix  the  fir>^t 
and  second  ril)s.  The  serrati  postici  .^nperiores?  help  to  fix  the 
second  rib,  and  raise  the  thir<l,  fourth,  and  fifth  riLs.  The  ex- 
ternal intercostals  and  interchondrals  and  the  levatores  costaruni 
elevate  and  evert  the  Hrst  to  the  tenth  ribs.  They  serve  also  to 
give  the  intercostal   tissue  a  proj>er  tension. 

During /brcerf  iiispiration  additional  muscles  are  brought  into 
play  to  i)ermit  a  more  powerful  inspiratory  act.  Besides  the 
muscles  already  enumerated,  the  following  are  brought  into  play: 
The  trapezei  and  rhoniboidei  fix  the  shoulders  ;  the  pect<jrales 
majores  and  minores,  acting  from  the  fixed  shoulders,  draw  the 
sternum  and  rii)s  upward  ;  the  sternomastoidea  fix  the  upper  part 
of  the  chest ;  the  erectores  spinie  stiffen  the  vertebral  column  ;  the 
serrati  postici  inferiores,  quadrati  lumborum,  and  sacrolumbales 
draw  the  lower  ribs  downward  and  backward. 

At  the  close  of  inspiration  the  various  muscles  that  raised  the 
thorax  gradually  relax,  and  by  its  weight  the  thorax  compresses 
the  lungs  and  expels  the  air.  In  addition  there  is  an  active  recoil 
of  the  elastic  tissue  in  the  substance  of  the  lung,  which  has  been 
put  on  the  stretch  during  inspiration.  Also  during  inspiration 
the  interosseous  portions  of  the  internal  intercostal  muscles  were 
put  on  a  stretch  ;  when  expiration  begins  these  muscles  contract, 
but  their  contraction  is  not  sufficiently  forcible  to  pull  the  ribs 
down,  and  the  only  purpose  of  this  contraction  seems  to  be  to 
keep  the  intercostal  tissues  tense  and  thus  prevent  bulging  of  the 
intercostal  spaces.  During  inspiration  each  costal  cartilage  is 
twisted  in  the  direction  of  its  long  axis  by  the  eversion  of  the 
ribs.  During  expiration  the  costal  cartilage  tends  to  untwist  itself. 
It  may  be  said  there  are  no  imiM-les  of  quiet  expiration.  Forced 
exjnration  is  accomplished  by  the  intervention  of  many  mus- 
cles. 

The  interosseous  internal  intercostals  act  forcibly  in  drawing 
down  the  ribs  when  the  lower  part  of  the  thorax  is  fixed  ;  the  ab- 
dominal muscles  fix  the  lower  part  of  the  thorax  and  press  the 
abdominal  contents  upward  ;  the  levatores  ani  an<l  perineal  mus- 
cles hold  the  fioor  of  the  pelvis  riirid  against  abdominal  pressure  ; 
the  triangularis  sterni  draws  the  costal  cartilages  down. 

A  number  of  movements  which  take  place  in  connection  with 


136  RESPIRATION. 

the  ingress  and  egress  of  air  to  the  lungs  are  known  as  associated 
respiratory  movements.  The  nostrils  may  dilate  with  inspiration 
and  return  to  their  passive  condition  with  expiration.  The  soft 
palate  moves  to  and  fro;  the  glottis  is  widened  and  narrowed. 
During  labored  breathing  the  mouth  is  opened  and  the  muscles  of 
the  face  become  active  ;  the  soft  palate  is  raised  and  the  larynx  is 
lowered. 

It  is  stated  that  of  the  two  types  of  respiration,  "thoracic"  and 
"abdominal,"  the  former  is  more  marked  in  women  and  the  latter 
in  men.  This  is  true  in  the  sense  that  women  increase  the  antero- 
posterior and  the  lateral  diameters  of  the  chest  more  than  do  men, 
owing  not  so  much  to  functional  differences  between  the  sexes,  as 
to  habits  of  dress,  etc.  Adult  males  and  children  of  both  sexes 
use  the  diaphragm  almost  exclusively  in  quiet  inspiration. 

When  the  ear  is  placed  in  contact  with  the  chest- wall  or  a  steth- 
oscope is  used,  a  respiratory  murmur  will  be  heard — fairly  marked 
during  inspiration  ;  short  and  faint  during  expiration.  It  varies 
in  different  parts  of  the  chest-wall,  being  loudest  over  the  large 
bronchi.  The  changes  in  these  murmurs  incident  to  disease  of  the 
respiratory  tract  are  characteristic  of  different  pathological  changes, 
and  it  is  upon  the  recognition  of  these  alterations  that  the  value 
of  auscultation  depends.  The  force  of  the  inspiratory  muscles  is 
greatest  in  people  of  medium  height,  being  equivalent  on  the 
average  to  a  column  of  mercury  three  inches  high.  It  diminishes 
in  people  above  and  below  this  height.  The  force  of  expiration  is 
about  one-third  greater  ;  but  the  variations  are  not  so  regular, 
since  the  expiratory  muscles  are  used  for  other  purposes,  so 
becoming  stronger.  The  value  of  breathing  through  the  nose 
instead  of  the  mouth  consists  in  that  it  warms  the  air  and  moistens 
it ;  foreign  particles  are  partially  removed  and  noxious  odors 
detected. 

Normal  respirations  may  be  studied  in  man  by  means  of  the 
stethograph  or  the  pneumograph  of  Marey.  It  is  found  that 
inspiration  and  expiration  follow  each,  other  without  pause ;  that 
inspiration  is  shorter,  and  that  the  curves  of  each  differ  in  minor 
respects  only.  In  pathological  cases  there  may  be  expiratory  or 
inspiratory  pauses.  The  Ghexjne-Stokes  respiration  consists  of 
groups  of  ten  to  thirty  respiratory  movements,  which  are  shallow 
at  first,  but  become  deeper  and  deeper  until  a  maximum  is  reached, 
after  which  they  gradually  become  shallow  again.     The  intervals 


RESrniATIOS. 


VM 


between  tlie  f^roupa  last  iVoin  thirty  to  forty-five  seeoiidH.  Tiie 
time-ratio  of  inspiration  to  expiration  may  W\  put  at  o  :  0.  lu 
infants  the  ratio  is  1  :  2  or  .">.  The  rair  of  respiration  vurietj  with 
the  most  diverse  internal  untl  external  eonditions.  In  tiie  normal 
adult  the  rate  is  about  18  cycles  a  minute  when  the  l)ody  is  in 
repose.  Tlie  ratio  to  the  pulse-rate  may  be  put  at  1  :  4.  During 
quiet  respiration  tlie  inflow  and  outllow  of  air,  wiiich  amounts  to 
about  aOO  c.e.,  or  30  cubic  inches,  is  known  as  the  tidal  air.  It 
does  not  go  lower  than  the  large  l)ronchi.  The  volume  of  expired 
air,  owing  to  its  increased  temperature,  is  greater  than  that  inspired, 
but  the  actual  quantity  is  less.  ( 'omjtlonoda/  air  (about  1  iJO{)  c.c.) 
is  the  amount  that  can  be  inspired  after  an  ordinary  iuspiratiou. 

Fig.  22. 


Tracinp  of  thoracic  respiratory  movements  obtained  by  means  of  Marey's  pneu 
mograph  (Fostcrt.  A  wliole  respiratory  jiliase  is  cvjinprised  between  n  and  a ;  in- 
spiration, during' which  the  lever  </esc«K/s,  extending  from  a  to  6,  and  expiration 
from  b  to  a.    The  undulations  at  c  are  caused  by  the  heart's  beat. 

The  snpplemenial  or  reserve  air  (about  1500  c.c.)  is  the  amount 
that  can  be  expelled  after  an  ordinary  expiration.  Residual  air 
is  the  volume  that  remains  in  the  lungs  after  the  most  forcible 
expiration  (1500  c.c).  Vital  capacity  is  equal  to  the  sum  of  the 
oomj)lemental,  tidab  and  sup|)lemental  air.  SfatitDiari/  air  is  the 
amoimt  that  remains  after  the  ordinary  ex])iration.  and  is  equal  (o 
the  sum  of  the  reserve  and  the  residual  air.  The  IiDig  capacitti  i:i 
the  total  quantity  of  air  that  can  be  held  after  th(>  most  forcible 
ins|)iration,  and  is  equal  to  the  sum  of  the  vital  capacity  and  re- 
sidual air  (4500  c.c. ). 

It  may  caMly  be  ca/eii/alcd  that  man  in  tn'ody-faur  hours  respires 
about  10,800  litres  of  air,  which  is  equal  to  a  space  71  feet  in 
three  dimensions.     The  ratio  of  the  quantity  of  (jxygen  absorbed 


138  BESPIBATION. 

to  the  carbon  dioxide  given  off  is  known  as  the  respiratory  quo- 
tient. While  in  the  lungs  the  air  loses  4.78  volumes  of  O^  in  100, 
and  gains  4.34  volumes  of  CO^  in  100,  so  that  the  value  of  the 

4.34   . 

respiratory  quotient,  ,  is  equal  to  0.901.     This  value  is  subject 

to  great  variations,  because  the  production  of  carbon  dioxide  is  to 
some  extent  independent  of  the  amount  of  oxygen  absorbed.  This 
is  so  for  several  reasons  : 

1.  COj  may  result  not  only  from  oxidation  changes,  but  from 
intramolecular  splitting,  so  that  the  elimination  of  CO^  in  normal 
quantity  may  continue  when  absorption  of  0^  has  entirely  ceased. 

2.  Some  food-stuffs  require  more  O^  for  their  complete  oxidation 
than  others. 

The  air  during  its  sojourn  in  the  lungs  is  altered  in  addition  to 
its  Og  and  CO^  contents  by  assuming  the  te^nperature  of  the  body, 
regardless  of  the  teviperature  of  the  outside  atmosphere ;  by  an 
increase  of  its  aqueous  vapor ;  and  by  the  jwesence  of  volatile  organic 
bodies.  The  nitrogen  remains  unchanged.  The  quantity  of  tvater 
lost  by  the  lungs  varies  inversely  with  the  amount  in  the  atmos- 
phere, and  directly  with  the  quantity  of  air  inspired.  The  blood 
in  its  passage  through  the  lungs  becomes  aerated.  The  O^  and 
COj  in  arterial  and  venous  blood  together  form  about  60  volumes 
of  the  blood  in  100.  The  proportions  of  the  gases  to  each  other 
are  constant  in  the  arterial  blood,  but  vary  in  the  venous  blood  in 
different  localities. 

The  oxygen  of  the  air  enters  the  alveoli  of  the  lung,  passes  into 
the  blood  through  the  delicate  epithelial  walls,  and  is  carried  to 
the  tissues,  where  it  is  taken  up  by  the  cells.  Very  little  is  used 
up  in  the  blood.  The  CO^  given  off  by  the  cells  is  carried  to  the 
alveoli  of  the  lungs  by  the  blood,  and  is  there  given  off.  But  the 
air  that  is  inspired  does  not  reach  the  alveoli  directly,  because  the 
lungs  are  never  completely  emptied  of  air.  It  becomes  necessary, 
therefore,  to  consider  the  methods  by  means  of  which  the  inter- 
change of  gases  is  brought  about.  The  air-currents  that  are  set 
up  mechanically  probably  help  to  equalize  the  composition  of  the 
air  in  the  lungs.  Besides,  the  heart  with  each  contraction  as  it 
shrinks  in  size  expands  the  lungs  slightly  and  causes  a  movement 
of  air  into  the  chest  synchronous  with  its  beat.  These  are  known 
as  cardiopneumatic  movements.  In  addition  to  the  mechanical 
factors,  the  physical  process  of  diffusion  is  of  great  importance. 


RESl'IlLlTloy.  139 

The  rapidity  of  diHusioii  depemls,  among  other  things,  upon  the 
dilii'r(Mi<'i.'H  ot"  the  partial  pri'ssiires  of  the  gases  in  various  regions. 
If  the  total  atmospheric  pressure  is  700  mm.  Ilg  and  ().^  forms 
1^  of  the  gaseous  constitueuts  of  the  air,  then  it  will  exert  a  press- 
ure of  its  own  equal  to  i  of  7G(),  or  lo2  mm.  Hg  ;  and  carhon 
dioxide,    forming   0.04   volume  in   100  of  the  air,   will   exert  a 

pressure  of  of  760,  or  about  0.30  ram.  Ilg.     It  has  heeu  esti- 

mated that  tiie  partial  pressures  of  O^  aud  CO„  in  alveolar  air  are 
equal  to  100  and  2o  mm.  Hg,  respectively.  The  difiereuces  in 
partial  pressures,  therefore,  will  cause  O.^  to  diffuse  toward  the 
alveoli,  aud  CO.,  from  the  alveoli  to  the  outside  air. 

The  f/nxe:^  in  the  blood  are  not  only  in  solution,  but  also  in  weak 
chemical  combination,  so  that  diffusion  from  the  alveoli  into  the 
blooil  and  vice  versa  is  somewhat  com[)licated.  The  amount  of  a 
gas  that  is  absorbed  when  lirought  in  contact  with  water  depends 
upon  the  relative  solahilifii,  the  temperature,  aud  the  baronidric 
pressure.  Eacli,  of  a  mixture  of  gases,  is  absorl)ed  independently 
of  the  others.  The  relative  solubility  is  expresseil  by  the  coeffi- 
cient of  a6.sor/j/io/i  of  the  fluid,  which  is  experimentally  determined, 
and  is  found  to  be  in  inverse  ratio  to  the  temperature  and  in  direct 
relation  to  the  pressure.  The  absorption-coefficient  of  water  for 
O^,  as  an  example,  at  zero  C/entigrade  and  7()0  mm.  pressure,  is 
equal  to  0.04S9.  This  means  that  under  the  given  conditions  of 
temperature  and  pressure  1  volume  of  water  will  take  up  0.04S9 
volume  of  O.,.  Since,  however,  the  O.,  forms  but  i  of  the  quantity 
of  the  air,  water  will  absorl)  from  the  atmosphere  only  i  of  0.0489 
volume,  which  is  equal  to  0.009-f ,  or  nearly  0.01  volume.  As 
the  partial  pressure  of  O^  is  raised  or  lowered,  O.,  will  leave  or 
enter  the  water,  so  that  the  gas  in  solution  is  said  to  be  under  ten- 
sion. The  absorption-coefficient  of  blood  for  O.,  is  about  that  of 
water,  but  at  the  bodily  temperature  is  decreased  to  less  than  i. 
Every  volume  of  blood  should,  therefore,  contain  •'  volume  of  oxv- 
gen  in  100  ;  but  experiment  shows  that  there  is  much  more  present. 
Upon  subjecting  blood  to  a  vacuum,  O,,  is  given  ofl'  according  to 
the  laws  of  partial  pressures  and  tensions  until  tiie  pressure  is 
lowered  to  -,',y  of  an  atmosphere.  From  -J^  to  ^^  of  an  atmosphere 
the  great  bulk  of  ().,  is  given  off.  Below  ■^^,  physical  laws,  as 
given  above,  again  prevail.  The  explanation  of  this  is  that  the 
O,  is  held  in  chemical   combination  with   the  hiemoijlobin,  antl   is 


140  RESPIRATION. 

set  free  at  J^  to  ^^  of  an  atmosphere.  This  pressure  is  termed 
the  tension  of  dissociation. 

Venous  blood  contains  45  volumes  of  GO^  in  100.  Of  this,  5 
per  cent,  is  in  simple  solution  ;  10  to  20  per  cent.,  in  firm  chemi- 
cal combination ;  and  75  to  80  per  cent.,  in  loose  chemical  combi- 
nation. The  largest  amount  is  connected  with  the  red  blood-cells. 
While  the  CO^  absorbed  by  water  increases  regularly  with  the 
increase  of  pressure,  that  absorbed  by  solutions  of  hsemoglobin  is 
relatively  large  for  low  pressures  and  small  for  high  pressures. 
The  quantity  in  the  blood  is  in  excess  of  what  physical  laws  will 
permit.  It  is  found  that  the  partial  pressures  of  O^  and  CO^  in 
venous  blood  are  about  22  and  41  mm.  Hg,  respectively.  Com- 
paring the  pressures  of  0^  in  the  lung,  alveoli,  blood,  and  tissues 
(152,  100,  22,  0),  with  those  of  CO,  (0.3,  23,  41,  58),  it  is  seen 
that  Oj  and  CO,  will  diffuse  in  opposite  directions.  Pure  oxygen 
at  a  pressure  of  1  atmosphere  may  be  breathed  without  injury. 
At  higher  pressures  it  acts  as  an  irritant  and  produces  inflamma- 
tion. When  less  than  13  volumes  of  oxygen  are  present  in  the 
air  in  100,  it  is  insufficient  to  maintain  the  life  of  man.  Pure 
COj  is  fatal  in  from  two  to  three  minutes.  N,  H,  and  CH^  cause 
no  inconvenience  if  sufficient  O^  is  present.  Nitrous  oxide  and 
ozone  produce  ansesthesia,  and  finally  death.  Air  containing  2 
volumes  of  CO,  in  100  is  rapidly  fatal. 

Eupnoea  is  normal,  easy  breathing.  Apnoea  is  a  condition  of 
suspended  breathing.  Hyperpnoea  is  increased  respiratory  activity. 
Polypncea  is  a  condition  of  deep,  labored  breathing.  Asphyxia  is 
characterized  by  convulsive  breathing,  followed  finally  by  infre- 
quent and  feeble  respirations.  Apnoea  can  be  induced  in  man  or 
animals  by  rapid,  deep  respiratory  movements  or  by  forcing  air 
into  the  lungs  with  a  bellows.  It  is  brought  about  by  using  pure  0, 
or  H., ;  lasting  for  a  longer  time  when  the  former  is  used.  But  the 
fact  that  it  can  be  produced  with  H,  shows  that  the  condition  can- 
not be  due  to  a  superabundance  of  0,  in  the  blood.  When  the 
vagi  are  cut,  H,  no  longer  brings  about  apnoea.  It  is  believed 
that  in  the  violent  inflation  of  the  lungs  the  sensory  endings  of 
the  pneurnogastric  in  the  lungs  are  stimulated,  which  produces  a 
temporary  paralysis  of  the  respiratory  centre.  The  increased 
amount  of  O,  in  the  alveoli  and  blood,  however,  prolongs  the 
condition.  Hyperpnoea  is  produced  usually  by  the  products  of 
muscular  activity  which  excite  the  respiratory  centre.    The  nature 


ni:si'i!:ATf(>y.  Ml 

of  thc-^e  products  is  unknown,  l)ut  tlie  «lecTeas((l  alkalinity  of  the 
blood  iudirates  that  tlu-y  may  he  of  an  aeid  cliaracler.  Polypnceu 
is  due  to  direct  stimulation  of  the  respiratory  ceutre  throuirh  the 
temjjerature  of  the  hlood  or  throuj,'ii  reflex  excitation  of  cutaneous 
nerves.  Dyspnua  may  he  the  result  of  a  deficiency  of  U^,  or  due 
to  an  excess  of  CO.,,  in  the  hlootl.  Oxygen  dyspn«ea  is  charac- 
terized hy  frequent  deep  inspirations  ;  carl)on  diijxide  dyspud-a, 
by  iufrequent,  viirorous  expirations.  In  the  former,  death  is 
severe  ;  there  is  a  marked  rise  of  blood-pressure  and  violent  con- 
vulsions. In  the  latter,  death  takes  place  more  quietly,  the 
bloofl-pressure  rises  less,  and  no  motor  disturbances  are  present. 
Cardiac  and  hemorrhagic  dyspnoeas  are  due  to  a  lack  of  0^  chiefl}'. 
Asphyxia  is  divided  into  three  stages — 

1.  One  of  hyperpua^a  ; 

2.  One  of  dyspnwa  and  convulsions  ; 

3.  One  of  collapse. 

If  asphyxia  is  brought  aliout  by  ligating  the  trachea,  the  proc- 
ess lasts  for  four  or  five  minutes.  The  first  stage  lasts  one  min- 
ute, the  second  a  little  longer,  and  the  third  from  two  to  three 
minutes.  If  produced  by  a  very  gradual  deprival  of  0.„  there 
may  be  no  motor  disturbances.  In  the  fii-st  stage  the  respirations 
are  increased  in  depth  and  frequency.  Inspiration  is  pronounced. 
During  the  second  stage  expirations  become  violent  and  convul- 
sive. During  the  third  stage  respirations  are  shallow,  the  pupils 
dilated,  motor  reflexes  disappear,  consciousness  is  lost,  convulsive 
twitches  are  present,  the  limbs  are  stretched  and  rigid,  the  head 
and  body  arched  backward,  and  finally  the  heart  ceases  beat- 
ing. During  the  first  and  second  stages  the  gums,  lips,  and 
skin  become  blue,  the  heart-beats  are  less  frequent,  and  the  blood- 
pressure  is  increased.  During  the  third  stage  a  general  depres- 
sion ensues.  After  death  the  hlood  is  almost  black,  the  arteries 
empty,  and  the  veins  and  lungs  congested.  Death  from  drowning 
is  due  usually  to  as|)hyxia,  but  sometimes  is  due  to  a  cessation  of 
the  activity  of  the  heart. 

The  rf.--jtiraton/  morrmenfs  have  a  marked  effect  ujioti  the  blood- 
pres^nre.  In  the  carotid  artery  with  every  ins|)iration  it  rises,  and 
with  every  ex))iration  it  falls  (Fig.  23).  The  two  events  are, 
however,  not  exactly  synchronous,  the  pre.<sure-changes  lagging 
a  little  beiiind  the  respiratory  changes.  The  effects  are  readily 
understood  when  it  is  remembered  that  the  thoracic  cavitv  is  an 


142 


RESPIRATION. 


air-tight  chamber,  and  that  the  elastic  fibres  of  the  lung  which 
fill  it  are  constantly  pulling  on  the  heart  and  bloodvessels.  This 
eifect  is  increased  during  inspiration  when  the  thorax  is  enlarged. 
The  pressure  of  the  blood  is  consequently  lowered  in  the  intrathoracic 
vessels,  and  the  blood  rushes  in  from  extrathoracic  regions,  where 
it  exists  under  atmospheric  pressure.  The  efiect  of  the  pull  of 
the  lungs  is  greater  upon  the  flaccid  walls  of  the  veins  than  upon 
the  more  rigid  walls  of  the  arteries,  so  that  the  inflow  through  the 


Fig.  23. 


Comparison  of  blood-pressure  curve  with  curve  of  intrathoracic  pressure  (Foster) 
(dog):  a  is  the  blood-pressure  curve  taken  by  means  of  a  mercury  manometer;  it 
shows  the  respiratory  undulation,  the  slower  beats  on  the  descent  being  very 
marked,  b  is  the  curve  of  intrathoracic  pressure  obtained  by  connecting  one  limb 
of  a  manometer  with  the  pleural  cavity.  Inspiration  begins  at  i,  expiration  at  e. 
With  the  beginning  of  inspiration  (i)  the  expansion  of  the  chest  causes  a  marked 
fall  of  the  mercury  in  the  intrathoracic  manometer  ;  but  the  effect  soon  diminishes, 
since  the  lessening  of  intrathoracic  pressure  does  not  bear  on  the  manometer  alone, 
but  on  the  lungs  also  ;  and  as  the  lungs  expand  more  and  more  the  fall  in  the  mer- 
cury becomes  less  and  less  until  toward  the  end  of  inspiration  the  curve  becomes 
very  nearly  a  straight  line.  Conversely,  the  return  of  the  chest  at  the  beginning  of 
expiration  (ei  produces  at  first  a  marked  rise  of  the  mercury  in  the  manometer;  but 
this  soon  ceases  as  the  air  leaves  the  chest  and  the  lungs  shrink,  whereupon  the 
mercury  falls  slowly. 

veins  is  favored  more  than  the  outflow  through  the  arteries  is 
hindered.  The  pulmonary  circulation  is  favored  also  by  the  in- 
creased negative  pressure  during  inspiration,  since  the  lung  fibres 
pull  with  greater  effect  on  the  pulmonary  veins  than  on  the  pul- 
monary artery,  which  produces  a  greater  difference  in  pressure  in 
the  two  vessels,  so  accelerating  the  flow  of  blood.  During  expira- 
tion there  is  not  only  a  return  to  the  former  condition,  but  the 
intrapulmonary  capillaries  are  actively  squeezed  between  the  air 
in  the  lungs  and  the  thoracic  walls.     This  again  aids  the  flow  in 


RKSriflATfON.  143 

its  passaijc  from  the  riL''lit  1(»  llic  id'l  siik'  ottlie  licarl.  '\\u'  press- 
un-  wliii'h  iii>pirali<iii  (liioiiirli  llu- (Icrici-iit  ot"  tlic  (liaplira^i-in  exerts 
on  the  alKloiuiiial  oriraiis  will  force  the  hlood  along  the  arteries 
toward  the  liinhsi  anil  cheek  somewhat  its  exit  from  the  thorax. 
Ill  like  manner  the  j)ressure  on  the  veins  will  force  the  hlood  into 
the  thorax  and  momentarily  cheek  its  flow  from  the  lower  ex- 
tremities. Finally,  the  heart-rate  is  increased  distinctly  during 
inspiration.  The  c()nd)ined  action  of  the  above  factors  is  to  draw 
an  increase<l  amount  of  hlood  into  the  thorax  ami  to  the  left  ven- 
tricle, which,  having  more  Mood  to  pump,  raises  the  hlood-preS-S- 
ure. 

Jifspi ration  continues  after  the  destruction  of  the  entire  brain 
excejd  the  hiilh.  The  location  of  the  centre  would  therefore  seem 
to  be  in  the  medulla,  but  its  exact  location  is  still  in  doubt.  It  is 
somewhere  in  the  lower  portion  of  the  bulb.  The  area  described 
by  Flourens  as  the  nauid  rital,  or  vital  knot,  consists  of  a  collec- 
tion of  nerve-Jibre-'<  which  arise  from  the  roots  of  the  tenth,  eleventh, 
ninth,  and  fifth  nerves.  The  centre  is  bilntrral,  one-half  being 
situated  on  each  side  of  the  median  line.  The  two  parts  are  in- 
timately connected  by  com)ni.<:.<iur(il  fibres,  but  may  be  se])arated  by 
a  section  in  the  median  line,  after  which  they  act  more  or  less  in- 
dependently of  each  other.  Each  half  is  connected  with  the  lung 
and  muscles  of  respiration  of  the  corresponding  side,  so  that,  if 
destroyed,  the  movements  on  its  own  side  cease.  If  one  pneumo- 
gaMric  nerve,  after  a  median  section  of  the  respiratory  centre,  is 
cut,  the  respirntiojiK  on  that  .^ide  are  sloirer  and  i)isj>irati<>ns 
become  vigorous.  When,  however,  the  cnmviissunil  fibres  are 
intact,  excitation  or  i))}iibition  of  one  side  afj'erts  the  otjier  as  well. 
After  section  of  one  vagus,  for  instance,  the  respiraiiunx  are  slower 
and  the  inspirations  stronger  on  both  sides.  Excitation  of  the 
central  end  of  the  cut  nerve  increases  the  respiratory  rate  of  both 
sides.  Each  half  of  the  centre  is  divided  into  an  inspiratorij  and 
an  expiraforti  portion.  Weak  stimulation  of  the  i)ixpirator;i  part 
increaxex  the  rate  of  breathing,  while  a  strong  sfimnlatio)i  arrests 
respiration  in  the  insjiirator;/  pha.se.  Stimulation  in  like  manner 
of  the  expiratory  part  of  the  centre  diminislies  the  rate,  and 
finally  causes  an  arrest  in  the  expiratorv  jiiiasc.  Ollirr  rrspiraton/ 
centres  have  been  described.  One  in  the  tuber  cinereum,  known 
as  the  polrjjmo'ic  centre,  is  excited  by  a  high  crternal  temperature, 
and  causes  a  very  rapid   rate  of  breathing.      Destruction  of  the 


144  RESFIRATION. 

tuber  ciuereum  stops  all  acceleration  by  heat.  A  centre  in  the 
optic  thalamus  in  the  floor  of  the  third  ventricle  is  excited  by  im- 
pulses from  the  nerves  of  sight  and  hearing.  It  is  an  accelerator 
centre.  Centres  have  also  been  described  in  the  anterior  and 
posterior  corpora  quadrigemina  and  in  the  brain-cortex.  The 
existence  of  these,  as  well  as  of  those  described  in  the  cord,  is 
doubtful. 

After  section  of  the  cord  in  the  cervical  region,  of  the  posterior 
roots  of  the  cervical  spinal  nerves,  of  the  medulla  from  all  parts 
lying  above  it,  of  the  vagi  and  glossopharyngeal  nerves,  the  respi- 
ratory movements  still  continue,  which  indicates  that  the  centre  is 
automatically  active.  The  rhythm  may  be  affected  by  the  ivill  and 
by  the  emotions,  by  the  quality  and  the  temperature  of  the  blood, 
and  by  afferent  impulses  coming  over  various  nerves,  but  particu- 
larly the  tenth.  Section  of  07ie  vagus  slows  and  deepens  the 
respiration.  Stimulation  of  the  central  cut  end  with  stimuli  of 
proper  strength  restores  the  rate,  if  it  does  not  further  increase 
it.  It  is  believed,  therefore,  that  while  the  blood  alone  may  bring 
about  rhythmical  discharges,  these  are  controlled  by  impulses 
coming  over  afferent  nerves.  Among  the  latter  are  the  fifth, 
ninth,  tenth,  and  various  cutaneous  nerves.  Excitation  of  the 
superior  laryngeal  fibres  causes  increased  expiratory  movements, 
and  perhaps  an  arrest  in  the  expii-atory  phase.  Excitation  of  the 
glossopharyngeal  nerves  has  a  similar  effect,  but  the  inhibitory 
influence  lasts  for  three  or  four  successive  respiratory  acts.  Irri- 
tating gases  affect  the  trigeminal  nerve-endings  in  the  nose  or  the 
endings  of  the  tenth  nerve  in  the  larynx  and  lungs.  The  effect 
of  the  excitation  of  the  cutaneous  nerves  may  be  seen  in  a  cold 
douche,  which  primarily  increases  the  respiratory  rate  and  may 
cause  its  cessation. 

The  efferent  respiratory  nerves  are  the  phrenics,  which  supply 
the  diaphragm ;  certain  spinal  nerves  supplying  respiratory  mus- 
cles, as  the  pneumogastrics.  Section  of  one  phrenic  causes  paraly- 
sis of  the  diaphragm  on  the  corresponding  side.  Section  of  the 
cord  just  below  the  fifth  cervical  nerve  stops  the  costal  movements, 
but  does  not  affect  the  diaphragm,  because  the  nuclei  of  origin  of 
the  phrenics  lie  just  above  the  section.  If  the  section  had  been 
placed  somewhat  higher,  respiration  ceases  entirely,  but  the  asso- 
ciated movements  of  the  larynx  and  face  continue.  During /orcec? 
breathing  the  facial,  hypoglossal,  and  spinal  accessory  nerves  are 


/v'A'.V/V/M  770.V.  145 

culled  into  action.  Diiriiiu^  iifrriiic  life  the  rrxjtiraionj  reiifre  is  in 
jin  iijiiKcif  condition,  on  account  ot"  a  loiv  Irrilnhi/ifi/  of  tlic  rrxj/i- 
Kitonj  centre  and  the  lar^c  amount,  relatively,  of  oxy<,a'n  in  the 
l)loo(l.  Cases  have  iii-en  seen  in  which  the  child  has  made  respi- 
ratory etibrts  while  within  the  intact  fcetal  niemhruues.  Such  au 
attem|)t  draws  some  (»f  the  anniiotic  fluid  into  the  nose,  causing 
inhibition  of  all  further  efforts.  After  birth,  iclien  xjKinfaiieon.i 
rexpinition  ix  about  to  take  place,  it  ix  well  to  roiwre  all  in  urns  or 
other  matter  from  the  iioxe,  to  avoid  inxpiration  of  them. 

The  nerves  which  are  distributed  to  the  linif/  tixxne  are  the 
piieiimoyaxfricx,  xijntpathetic,  and  dorsal  nerves.  Among  the 
jineumogastric  fibres  are  broncJioconstrictors  and  bronchodilatorx. 
Excitation  of  one  vac/us  causes  a  constriction  of  the  brouchi  of 
both  lungs  ;  section  of  the  nerve  causes  a  dilatation  of  the  bronchi 
iu  the  corresponding  lung  ;  stiviulation  of  both  peripheral  and 
central  ends  of  the  cut  nerve  causes  constriction  of  the  bronchi  of 
both  lungs,  which  is  more  pronounced  with  the  stimulation  of  the 
peripheral  end.  Asjthi/xia  causes  bronchoco)ixfrlctioii,  ])nt  not  after 
the  vagi  are  sectioned.  The  sympathetic  fibres  are  trophic  and 
vasomotor  in  function. 

There  are  a  num])er  of  involuntary  and  voluntary  special 
respiratory  acts,  largely  reflex,  which  result  from  modifications  of 
inspiration  and  expiration. 

Sighing. — This  results  from  a  prolonged  inspiration,  the  air 
passing  noiselessly  through  the  larynx  and  being  expelled  rather 
suddenly. 

Hiccough. — This  resembles  sighing,  but  the  inspiration  is 
sudden,  due  to  a  spasmodic  action  of  the  diaphragm. 

Cough. — This  results  from  a  deep  ins]>iration  followed  by  a 
forced  and  sudden  expiration,  during  which  the  glottis  is  closed 
momentarily  by  the  s|3asmodic  action  of  the  vocal  cords. 

Sneezing. — In  this  case  after  a  deep  inspiration  the  air  is  di- 
rected through  the  nasal  passages  by  a  sudden  and  forced  vxytx- 
ration. 

Speaking. — In  this  case  there  is  a  voluntary  expiration,  ami  the 
vocal  cords  ])eing  rendered  tense  by  their  musch's  vibrate  as  the 
air  passes  over  them,   proilucing  sound. 

Singing. — This  varii'S  from  speaking  only  iu  the  dificring  ten- 
sion and  position  of  the  vocal  cords,  and  the  consequently  difierent 
sounds  produced. 

10— Phys. 


146  RESPIRATION. 

Sniffing. — This  results  from  rapid  repeated  but  incomplete  nasal 
inspirations. 

Sobbing. — Tiiis  consists  of  a  series  of  convulsive  inspirations, 
during  which  the  glottis  is  more  or  less  closed. 

Laughing. — This  results  from  a  series  of  short  and  rapid  expi- 
rations. 

Yawning. — This  is  an  act  of  inspiration  more  or  less  involun- 
tary accompanied  by  a  stretching  of  various  facial  muscles. 

Sucking. — This  is  caused  chiefly  by  the  depressor  muscles  of  the 
OS  hyoides,  which,  by  drawing  down  and  back  the  floor  of  the 
mouth,  produces  a  partial  vacuum  in  it.. 

QUESTIONS  ON  CHAPTER  IX. 

What  two  different  meaniugs  are  included  in  the  term  respiration? 

What  purpose  do  the  lungs  of  man  serve  ? 

What  is  the  total  area  of  the  alveoli  of  the  lung? 

What  is  the  condition  of  the  lungs  before  birth? 

What  are  inspiration  and  expiration  ? 

Why  do  the  lungs  follow  the  walls  of  the  thorax? 

In  what  directions  is  the  thorax  enlarged  in  inspiration  ? 

Why  does  the  air  enter  the  lungs  in  inspiration  ? 

Tell  in  detail  by  what  mechanism  the  thorax  is  enlarged  in  inspiration. 

What  are  the  chief  muscles  of  inspiration  ? 

Give  the  action  of  each. 

How  is  expiration  brought  about  ? 

Give  the  action  of  the  muscles  of  forced  expiration. 

What  are  associated  respiratory  movements? 

Describe  the  character  and  significance  of  respiratory  sounds. 

What  is  the  force  of  the  respiratory  muscles  equal  to? 

What  is  the  value  of  nasal  breathing  ? 

Describe  a  respiratory  tracing. 

Describe  the  Cheyne-Stokes  respiration. 

What  are  the  relative  lengths  of  inspiration  and  expiration  ? 

What  is  the  rate  of  breathing,  and  how  is  it  varied  ? 

Define  and  give  values  of  tidal  air;  complemental  and  supplemental  air; 
residual  air  and  vital  capacity. 

What  is  the  stationary  air  equal  to  ? 

What  is  the  lung  capacity  ? 

What  volume  of  air  passes  through  the  lungs  of  man  in  a  day? 

What  is  the  respiratory  quotient?     Explain  why  it  varies. 

How  is  the  air  altered  in  the  lungs  ? 

How  does  the  quantity  of  water  vapor  given  off  by  the  lungs  vary? 

How  is  the  carbon  dioxide  held  in  the  blood? 

What  is  the  evidence  that  CO2  is  held  in  chemical  combination? 

Compare  the  partial  pressures  of  O2  and  CO2  in  the  external  air,  alveoli, 
blood,  and  tissues. 

What  is  the  efl'ect  of  breathing  pure  oxygen  ? 

Give  the  effects  of  breathing  other  gases. 


QUESTIONS  OX  ClIAPTKn    fX.  147 

Define  the  terms— eupucea,  apnuea,  liypcrpua'a,  polypna'a,  dyspncea,  aud 
asi)h.vxia. 

Discuss  apna^i  and  its  eanses. 

IIiiw  is  liyperiUKi-a  i)r(ithiced? 

lli(\v  is  iiolyjind'a   produced? 

Wliat  is  dy>piia-a  dnc  to',' 

Discuss  asjihyxia  in  detail. 

What  is  (hath  l)y  drowuinK  due  to? 

(Jive  the  tiiiie-rehilions  of  the  respiratory  movements  to  the  respiratory 
hiood-pri'ssure  chaiij;es. 

Kx])iain  in  detail  how  respiratory  movements  produee  changes  in  blood- 
])ressure. 

What  are  the  changes  in  the  heart-rate  during  respiration? 

Discuss  the  resi)ii-iUory  centre  in  the  medulla. 

What  can  he  said  of  other  resi)iraliiry  centres? 

What  is  the  proof  that  the  bulbar  resi)iratorj'  centre  is  automatically 
rhythmic? 

What  happens  to  the  blood  in  its  passage  through  the  lungs? 

What  is  the  amount  of  O2  and  CO2  in  the  blood? 

What  factoi-s  bring  the  O2  of  the  air  to  the  alveoli  of  the  lung? 

What  are  cardiopiieuiiiatic  movements? 

Exjilain  what  is  meant  Ity  the  jtartial  pressure  of  a  gas. 

Exi>lain  iu  detail  the  diti'usion  of  O2  from  the  outer  air  into  the  alveoli. 

In  what  ways  are  the  gases  of  the  blood  held  ? 

W'hat  factors  govern  the  amount  of  a  gas  ab.sorbed  by  a  liquid? 

What  is  meant  by  the  coefficient  of  absorption  ? 

What  is  the  absorption-coetHcient  of  serum? 

In  what  way  is  the  gas  in  the  blood  under  tension? 

How  much  oxygen  should  the  blood  take  up  according  to  physical  laws? 
Does  it  in  reality  hold  more  or  less? 

How  is  the  discrepancy  explained? 

What  is  meant  by  tension  of  dissociation? 

How  may  the  respiratory  rhythm  be  affected? 

What  is  the  effect  upon  the  respiration  of  sectioning  the  vagi?  Of  stimu- 
lation of  the  central  end? 

What  are  the  aflferent  nerves  that  control  the  activity  of  the  respiratory 
centre? 

What  is  the  effect  of  excitation  of  the  superior  laryngeal  and  glossopharyn- 
geal nerves  ? 

Through  what  nerves  do  irritating  gases  affect  respiration? 

What  afferent  nerves  are  involved  in  respiration? 

What  is  the  effect  of  sectioning  a  phrenic  ner%e? 

Give  the  effect  of  sectioning  tlio  cord  just  below  the  fifth  spinal  nerve. 

Discuss  the  condition  of  the  res]>iratory  centre  in  the  frctus. 

What  nerves  are  distributed  to  the  lung  tissue  ? 

Discuss  the  kinds  of  filires  in  the  vagus  which  are  supplied  to  the  bronchi. 

Wliat  does  stimulation  of  the  central  and  peripheral  ends  of  tiie  fibres 
l>ring  about? 

Define — sighing,  hiccough,  cough,  sneezing,  speaking,  singing,  sniffing, 
sobbing,  laughing,  yawning,  and  sucking. 


148  ANIMAL  HEAT. 

CHAPTER   X. 

ANIMAL   HEAT. 

Warm-blooded  and  cold-blooded  animals  are  respectively 
designated  as  homothermous  and  poikilothermous.  The  former 
have  a  body-temperature  that  varies  very  little  from  a  certain 
normal  which  is  characteristic  for  the  species,  while  the  temperature 
of  the  latter  varies  directly  with  the  medium  in  which  they  live, 
although  usually  from  a  fraction  to  several  degrees  higher.  Man 
is  warm-blooded — the  normal  temp)erature  being  about  98.5°  F. 
(37°  C).  The  temperature  is  not  invariable,  and  in  the  internal 
organs  may  be  as  high  as  100°  F.  under  normal  conditions.  In 
the  rectum  the  temperature  is  about  1  degree  F.  higher  than  in 
the  mouth  or  armpit.  The  warmest  blood  in  the  body  is  that  com- 
ing from  the  liver  during  digestion,  and  the  coolest  is  that  comwig 
from  exposed  parts,  such  as  the  tips  of  the  ears  and  the  nose.  In 
health  the  temperature  varies  slightly  with  the  external  temperature, 
age,  exercise,  sex,  constitution,  etc.  The  temperature  of  a  newborn 
child  is  about  37.86°  C.  In  the  adult  there  is  a  diurnal  variation 
of  1  to  1.5  degrees  F. ;  being  lowest  in  the  morning  and  highest  late 
in  the  afternoon.  This  corresponds  to  the  usual  temperature-ranges 
in  fever.  In  ordinary  pathological  conditions  the  temperature 
does  not  remain  long  at  a  point  below  95°  F.  nor  above  105°  F. 
without  fatal  results.  Under  conditions  of  prolonged  exposure  to 
cold  and  the  algid  stage  of  cholera,  recovery  has  occurred  after  a 
bodily  temperature  as  low  as  75°  F.  On  the  other  hand,  in  some 
cases  of  extreme  fever,  as  from  sunstroke,  recovery  has  been  noted 
after  a  temperature  of  110°  to  112°  F. 

It  has  been  proved  that  the  source  of  animal  heat  is  the  potential 
energy  of  the  foods.  The  latter  is  converted  into  heat  either 
directly  as  the  result  of  chemical  decompositions  or  indirectly 
through  muscular  movements,  friction,  etc.  About  90  per  cent,  is 
formed  directly.  The  heat  liberated  by  an  animal  may  be  meas- 
ured by  calculating  the  potential  energy  from  the  food  ingested  or 
from  the  amounts  of  oxygen  absorbed  and  carbon  dioxide  given  off. 
This  is  indirect  calorimetry.  Direct  calorimetry  consists  in  meas- 
uring the  heat  directly  by  means  of  a  calorimeter.  A  calorimeter 
is  an  apparatus  by  means  of  which  the  amount  of  heat  given  off 


ANIMAL  HEAT.  149 

bv  an  anirnjil  may  be  luea^juriHl.  It  usually  consii?ts  of  two  cou- 
ceutric  c'a.<i';i  st'paratetl  by  ice,  air,  or  water,  ami  provided  with 
tlieriuometers  and  giusoiueters  so  arranged  as  to  insure  proper  ven- 
tilation to  the  animal  which  is  placed  in  the  inner  case.  The  object 
ot"  calorinietry  is  to  determine  the(|nantity  of  heat  that  is  dissipated 
in  a  detinite  time.  A  certain  amount  ot"  tiie  heat  is  taken  up  by 
the  apjKiratus.  some  is  given  to  the  air  that  passes  tlirough  the 
calorimeter,  and  tinally  some  is  lost  in  the  evaporation  of  water. 

To  determine  the  amount  imparted  to  the  ap|)aratus,  it  is  neces- 
sar\'  l)etbre  using  to  determine  its  calorimetric  equivalent,  which  is 
done  by  burning  alcohol  within  it  until  the  temperature  has  been 
raiseil  1  degree  C  One  gramme  of  alcohol  will  yield  about  7000 
calories  of  heat,  so  that  if  5  grammes  of  alcohol  are  requiretl  to  raise 
the  temjierature  of  the  calorimeter  1  degree  C.  then  the  tpiantity 
of  heat  absorl»ed  would  be  equal  to  5  times  7000,  or  o-3,000  cal- 
ories. This  is  the  calorimetric  equivalent.  If  an  animal  has  raised 
the  temj>erature  of  the  calorimeter  10  degrees  C,  the  (juantity  of 
heat  that  it  has  given  otf  would  be  equal  to  10  times  the  calorimetric 
equivalent,  or  to  350  kilogramme-tlegrees.  The  quantity  of  heat 
given  to  the  air  is  determined  by  measuring  the  amount  of  air 
passing  through  the  calorimeter,  and  its  temjierature  on  its  entrance 
and  exit.  The  volume  of  the  air  must  be  corrected  for  the  increased 
temj>erature  and  then  reduced  to  weight,  after  which  it  is  multi{)lied 
by  the  sjiecitic  heat  of  air  at  0°  C,  and  then  by  the  number  of 
degrees  of  the  increase  of  temperature.  By  ■•^prcijic  heat  is  meant 
the  heat  required  to  raise  the  temperature  of  any  substance  1  de- 
gree C,  and  is  usually  compared  to  water  as  a  standard.  The 
specific  heat  of  the  animal  body  is  about  0.8.  The  formula  for 
the  correction  of  the  volume  of  air  is : 

V  P 


760  (1  -^  0.003665O  * 

V  is  ob.*ervefl  volume  at  0°  C  and  760  nmi.  Hg  ;  T',  dei^ired 
volume  at  0°  C.  and  760  mm.  Hg  ;  P,  observed  pressure  ;  antl 
/,  mean  temperature.  The  value  of  760  ( 1  -\-  0.0086(>5 )  is  ol> 
tained  from  standard  tables  while  the  barometric  pressure  and 
aqueous  tension  are  omitted,  being  too  small  to  produce  apprecia- 
ble error.  A  litre  of  dry  air  at  0°  C.  weighs  0.0012113  kilo- 
gramme. 


150  ANIMAL  HEAT. 

The  measurement  of  the  aqueous  vapor  of  the  air  before  enter- 
ing and  after  leaving  the  calorimeter  gives  the  data  for  the  estima- 
tion of  the  heat  lost  through  evaporation.  If  it  is  found  that  the 
total  quantity  of  water  evaporated  from  the  animal  is  100  grammes, 
it  is  only  necessary  to  multiply  by  582  (since  it  requires  this  num- 
ber of  calories  to  evaporate  1  gramme  of  water),  in  order  to  obtain 
the  heat  in  kilogramme-degrees  that  is  lost  by  evaporation.  The 
principal  part  of  the  total  heat  produced  by  the  body  is  generated 
by  muscular  activity. 

Subsidiary  sources  are  the  chemical  action  going  on  during  diges- 
tion, friction  of  muscles,  blood,  warm  foods,  sun's  rays,  etc.  In 
calorimetric  determinations  these  are  neglected. 

Throughout  life  the  body  maintains  a  constant  temperature,  so 
that  there  is  a  regulation  of  heat  produced  and  heat  dissipated. 
The  production  of  heat  is  known  technically  as  thermogenesis ;  the 
dissipation  of  heat,  as  thermolysis ;  and  the  regulation  of  the  rela- 
tions between  them,  as  thermotaxis.  It  is  evident  that  if  thermo- 
genesis and  thermolysis  vary  together,  the  body-temperature  will 
remain  unchanged  ;  but  an  increase  in  thermogenesis  with  a  con- 
stant or  decreased  thermolysis  will  raise  the  body-temperature. 
Further,  a  decrease  in  thermogenesis  with  constant  or  increased 
thermolysis  will  lower  the  body-temperature.  The  production  of 
heat  probably  takes  place  in  all  the  tissues  of  the  body,  since  they 
all  undergo  oxidative  changes,  but  the  muscles  are  the  main  source 
of  the  heat  not  only  when  active,  but  when  at  rest.  During  activ- 
ity the  greater  part  of  their  chemical  energy  is  liberated  as  heat, 
only  one-fifth  appearing  as  mechanical  energy.  The  work  of  the 
heart  is  entirely  converted  to  heat,  forming  about  5  to  10  per  cent, 
of  the  total  amount  produced  in  the  bod3^  It  is  known  that  when 
a  muscle  is  separated  from  the  central  nervous  system  it  continues 
to  produce  heat,  but  much  less  than  before.  Specific  thermogenic 
fibres  have  not  been  isolated.  It  has  been  claimed  that  the  act  of 
shivering  has  as  its  only  purpose  the  production  of  heat,  so  that  if 
the  muscular  contractions  of  shivering  are  brought  about  by  im- 
pulses passing  over  ordinary  motor  nerves,  they  must  have  a  spe- 
cific thermogenic  function.  The  proofs  of  thermogenic  ceritres  are 
the  following : 

1.  Excitation  of  the  skin  by  heat  or  cold  brings  about  changes 
in  heat-production  entirely  independent  of  vasomotor  changes. 

2.  Injury  or  excitation  of  certain  parts  of  the  brain  is  followed 


QUESTloys   <).\   CIIAl'Th'R   X.  151 

bv  increase*!  heat-production  ;  excitation  of  other  parts  of  the 
bruin,  by  u  decrease  of  lieat-|)njduction. 

8.  Injury  to  tlie  spinal  cord  brings  alioul  ciian<.'c.<  in  thenno- 
genesis  without  viUsoniotor  disturbances. 

4.  Operations  upon  certain  parts  of  the  cerel)ro8pinai  axis  lead 
to  an  increase  or  decreiuse  in  tlie  carbon  dioxide  excreted. 

Of  tiie.se  centres,  those  that  increase  tiiernio^enesis  are  called 
thermo-arrrlcrator  centres,  while  those  that  diminish  therniof.'enesis 
are  called  (Iwrmo-inJiilntonj  centres.  These  two  kinds  act  upou 
and  govern  a  third  kind  of  centre,  called  (jeiwral  or  automatic 
centres.  The  latter  are  located  in  the  sjnnal  cord.  The  thermo- 
accelerator  centres  probably  exist  in  the  caudate  nuclei,  pons,  and 
bulb.  The  inhibitory  centres  have  been  located  in  the  dog  in  the 
sulcus  craciatus  and  at  the  junction  of  the  nuprufujlvian  and  post- 
st/li'ian  fiiisures.  Ciianges  in  the  external  temperature  or  in  the 
temperature  of  the  blood  affect  the  centres  in  the  brain,  which  in 
turn  act  upon  the  general  centres  in  the  anterior  cornu  ol'  the  gray 
matter  of  tlie  cord.  Heat  intiueuces  the  thermo-inhibitory,  and 
cold  the  thermo-accelerator  centres. 

Heat  is  lost  by  an  organism  through  radiation  and  conduction 
from  the  skin,  by  the  evaporation  of  water  from  the  skin  and  lungs, 
and  in  warming  food  and  inspired  air.  Thermoli/iiis  is  brought  about 
by  complex  mechanisms.  If  the  temperature  of  the  bodv  becomes  too 
hi(/h,  the  actlritij  of  the  heart  is  increased,  peripheral  vascular  dilata- 
tion takes  place,  there  are  increased  respiratory  acfirify  and  secretion 
of  ■•(iveat.  These  processes  all  tend  to  increase  the  losi^  of  heat. 
When  the  external  temperature  becomes  excessive,  thennotaxis 
fails.  Cold,  for  instance,  may  cause  heat-dissipation  to  take  place 
more  rapidly  than  heat-px-oduction,  so  that  the  tem))erature  of  the 
body  continually  decreases  until  death  ensues.  The  post-mortem 
rise  of  temperature  is  due  to  the  fact  that  chemical  activity  will 
continue  in  the  tissues  for  some  time  after  the  mechanisms  of 
thermolysis  have  been  rendered  incompetent. 

QUESTIONS  ON  CHAPTER  X. 

Define  the  terms  honiotlu-rmotis  and  pnikilothcrmous. 

(live  the  bi>(ly-tciii)ieratiirc"  of  mail. 

In  what  ways  ilncs  it  vary? 

Where  are  the  warmest  ami  tlie  cnhlest  hlood  of  the  body  to  be  found? 

What  factors  iiillueiiee  h()(ly-temi>erature? 

What  is  the  source  of  tlie  energy  of  heat? 


152  NERVE  AND  MUSCLE. 

What  percentage  of  heat  is  directly  formed  from  the  chemical  energy  of 
the  food  ? 

What  are  direct  and  indirect  calorimetry  ? 

Describe  a  calorimeter. 

Describe  fully  how  the  calorimetric  equivalent  is  obtained. 

Why  is  it  necessary  to  obtain  the  calorimetric  equivalent  in  calorimetry  ? 

Explain  in  detail  how  the  heat  lost  to  the  air  is  calculated. 

What  is  the  specific  heat  of  a  body  ? 

Explain  how  the  heat  lost  by  evaporation  of  water  is  obtained. 

What  organs  are  principally  concerned  in  heat-production  ? 

What  subsidiary  sources  of  heat  are  there? 

How  much  heat  does  the  heart  produce  ? 

Define  thermogenesis,  thermolysis,  and  thermotaxis. 

Discuss  thermota.xis. 

What  is  the  eflect  upon  heat-production  when  a  muscle  is  separated  from 
the  central  nervous  system  ? 

Discuss  the  phenomenon  of  shivering. 

What  is  the  proof  that  thermogenic  centres  exist? 

What  classes  of  thermogenic  centres  are  there,  and  where  are  thev 
located?  •' 

How  is  thermolysis  brought  about? 

Explain  the  post-mortem  rise  of  temperature. 


CHAPTER  XI. 

NERVE  AND  MUSCLE. 

Most  of  the  cells  of  the  body  in  the  division  of  labor  have 
developed  preeminently  some  one  or  other  of  the  fundamental 
properties  of  protoplasm.  Thus,  muscle  is  characterized  by  con- 
tractility, but  has  not  entirely  lost  the  properties  of  nutrition,  con- 
ductivity, and  irritability.  Nerves  are  characterized  by  their  con- 
ductivity, but  possess  also  nutrition  and  irritability.  Both  muscle 
and  nerve  in  the  adult  condition  have  lost  the  power  of  reproduc- 
tion. The  properties  that  they  possess  in  common  are  irritability, 
conductivity,  and  nutrition.  The  phenomena  of  muscle  and  nerve 
can  best  be  studied  in  cold-blooded  animals.  The  frog's  gastroc- 
nemius (Fig.  24)  is  usually  the  most  convenient,  and  when  the 
sciatic  nerve  supplying  the  muscle  is  dissected  out  carefully  at  the 
same  time  there  results  a  nerve-muscle  preparation.  If  the  nerve 
of  such  a  preparation  is  in  any  manner  excited,  the  muscle  re- 
sponds by  a  sharp  and  quick  contraction  or  twitch.  The  excita- 
tion of  the  nerve  has  given  rise  to  a  disturbance  of  unknown 
nature  in  the  substance  of  the  nerve,  which  passes  rapidly  along 


NERVE  AM)  MUSCLE. 


153 


its  length  to  the  motor  cvd-plalr  and  rrcitis  tlio  innxcle-jibre,  which 
responds  l»y  its  eharacti'rislic  fit  net  ion,  coiitniclioii.  Tiiat  muscle 
in  irrilahh  independently  ot"  nerves  issliown  in  a  number  of  ways  : 
1.  Ihj  the  Curare  J'Jx/xrtmciif. — Tiiis  is  made  as  follows :  De- 
stroy the  brain  of  a  frog,  hy  pithing,  and  tie  off  all  the  structures 
of  the  left  leg  with   the  exception  of  the  sciatic  nerve.      Inject  a 

Via.  24. 


A  muscle-nerve  preparation  (Foster):  m,  the  nuisck',  pustrocnemiiis  of  frog;  n, 
the  sciatic  nerve,  all  the  branches  beinvrcut  away  except  that  sui>plyin>;  the  muscle  ; 
/.femur;  c^, clamp;  /.  n.,  tendo  .Achilles  ;  .f;).  c,  end  of  s:>inal  ciiuai. 

sufficient  amount  of  curare  solution  to  destroy  the  reflex  ruove- 
nients  of  the  right  leg  when  the  toe  is  pinched.  U)ion  trial  it 
will  he  found  that  Ktinin/afion  of  the  right  i^rinti'-  nerve  when 
severed  from  the  cord  calls  forth  no  movements,  while  rj-rltofion  of 
the  ff'ft  .sciatic  does  cause  movements  of  the  corrospomling  leg. 
TF7i''»  the  >ifimuhif<  i.<  applied  ilirecthi  to  the  »i (/.^'cA.s',  theij  both 
rrftpond.     The  drug  curare  has  destroyed  the   motor  end-plates. 


154 


NERVE  AND  MUSCLE. 


so  that  nervous  excitation  of  the  muscle  can  no  longer  take  place 
and  the  muscle-substance  is  stimulated  directly. 

2.  The  sartorias  muscle  of  the  frog  contains  no  nerve-fibres  at 
its  tips,  which  nevertheless  are  excitable. 

3.  The  heart  of  the  embryo  beats  rhythmically  before  nerve- 
fibres  are  developed. 

4.  Muscle  whose  motor  nerve  has  degenerated  as  the  result  of 
previous  section  is  excitable.  When  such  a  muscle,  when  dying, 
is  struck  sharply,  there  arises  a  local  swelling,  called  an  idiomus- 
cular  contraction. 

An  irritant  or  stimulus  is  any  external  influence  which  can 


Fig.  25. 


Diagram  of  an  induction  coil  (Foster) :  +  positive  pole,  end  of  negative  element ; 
—  negative  pole,  end  of  positive  element  of  battery;  K,  Du  Bois-Reymond's  key; 
pr.  c,  primary  coil,  current  shown  by  feathered  arrow ;  sc.  c,  secondary  coil,  current 
shown  by  unfeathered  arrow.    ' 


excite  living  matter  to  action.  There  are  five  classes  of  irritants  : 
mechanical,  thermal,  electrical,  chemical,  and  physiological.  The 
effect  they  produce  upon  living  matter  depends  not  only  upon  their 
efficiency,  but  also  upon  the  irritability  of  the  living  material 
on  which  they  act.  The  most  desirable  stimulus  for  experimental 
purposes  is  the  electrical  current,  which  produces  very  little  injury 
and  may  be  finely  graded  as  to  strength,  time,  and  place  of  appli- 
cation. It  may  be  either  a  constant  or  an  induced  current.  The 
former,  also  called  a  voltaic  current,  is  such  as  is  furnished  by  any 
cell  like  the  Grove  or  Daniell.  The  latter  is  obtained  by  the 
use   of  an  induction  coil    (Fig.   25).     This  instrument  consists 


NERVE  AM)  Mi'SCLE.  155 

essentially  of  two  coils  of  copper  wire,  one  ofwlii<-h  is  placed 
within  the  other,  hut  htiirrcn  irlilrh  tlirre  in  no  mclallir  contirclion. 
The  inner  coil  of  heavy  wire  (  pmnanj  roil )  is  connected  with  a 
source  of  electricity,  like  a  cell.  The  enrls  (»f  the  outer  coil  (ncc- 
oiidanj  coil),  which  consists  of  many  turns  of  line  wire  carefully 
insulated,  are  connected  with  electrodes,  hy  means  (jf  which  the 
induce<l  current  is  applied  to  the  tissues  to  he  stimulated.  Any 
chan<;e  in  the  streni;th  of  the  primnry  current — /.  e.,  the  (;urrcnl 
furnished  hy  the  voltaic  cell — hrin<,'s  about  a  change  of  potential 
in  the  outer  coil,  which  nuiiiifests  itself  as  the  induced  or  xccondary 
current.  This  gives  a  strong  shock  of  momentary  duration  and 
produce's  less  injury  than  the  voltaic  current. 

The  shock  resulting  from  closure  of  the  primary  current  is 
called  the  closiwj  xhock,  while  that  from  the  opening  is  called  the 
opening  shock.  With  the  constant  current  the  fonner  is  more 
effective  than  the  latter.  The  opposite  is  true  of  the  induced  cur- 
rent. The  cause  of  this  ditlerence  lies  in  the  construction  of  the 
induction  coil.  As  the  current  passes  along  each  turn  of  wire 
forming  the  primary  coil  it  excites  an  "induced"  current  in  the 
neighboring  turn  of  wire,  which,  having  an  o])posite  direction  to 
the  primary  current,  opposes  it,  and  therefore  delays  it  in  reaching 
its  maximum  strength  ;  but,  when  the  primary  current  is  broken, 
both  it  and  the  induced  currents  in  the  neighboring  turns  of  wire 
have  the  same  direction  and  do  not  oppose  each  other.  Since  the 
intensity  of  the  induced  current  with  the  same  strength  of  primary 
current  tlepends  upon  the  rapidity  with  which  the  primary  reaches 
its  maximum,  it  follows  that  the  cloxing  induced  current  must  be 
weaker  than  the  openinrj,  and  have  consequently  a  smaller  .<fimu- 
latincj  effect. 

The  effect  of  a  stimulus  is  proportional  to  the  rate  with  which 
it  reaches  its  maximum.  This  is  true  only  within  limits,  for 
a  stimulus  may  be  applied  both  too  slowly  and  too  quickly  to 
produce  any  effect.  This  has  been  expressed  in  Du  Rois-Key- 
mond's  law  :  "It  is  not  the  absolute  value  of  the  current  at  each 
instant  to  which  the  motor  nerve  replies  by  a  contraction  of  its 
muscle,  but  the  alteration  of  this  value  from  one  moment  to 
another;  and,  indeed,  the  excitation  to  movement  which  results 
from  this  change  is  greater  tiie  more  rapidlv  it  oceurs  l)y  eipKil 
amounts,  or  the  greater  it  is  in  a  given  time."  This  law  is  not 
strictlv  true. 


156  NERVE  AND  MUSCLE. 

The  denser  the  current  the  greater  is  its  stimulating  effect. 
This  is  well  illustrated  by  the  phenomena  of  unipolar  action. 
Usually,  in  order  to  stimulate  a  preparation  with  an  electrical 
current,  it  is  necessary  that  there  shall  be  a  complete  circuit ;  but 
under  certain  circumstances  one  wire  of  a  secondary  coil  leading 
to  the  nerve  is  sufficient  to  excite  it  when  the  primary  circuit  is 
opened.  This  may  be  explained  by  the  assumption  of  an  elec- 
trical charge  generated  in  the  secondary  coil  and  passing  through 
the  nerve  to  the  muscle.  In  its  transit  through  the  nerve  it 
arouses  a  nerve-impulse.  If  the  electrode  represented  by  the 
wire  on  which  the  nerve  rests  be  replaced  by  a  sheet  of  gold  foil 
which  is  made  to  touch  the  nerve  and  muscle  along  their  entire 
length,  the  charge  from  the  induction  coil  will  reach  all  points  of 
the  preparation  at  practically  the  same  instant  and  will  not 
excite  it.  The  charge  remains  of  the  same  strength,  but  the  elec- 
trodes alter  the  density. 

The  duration  of  a  stimulus  must  be  of  sufficient  length  to  pro- 
duce an  effect.  In  the  experiments  of  Tesla,  where  powerful  alter- 
nating currents  are  passed  through  the  body  without  injury,  it  is 
the  exceedingly  small  duration  of  the  changes  that  prevents  harmful 
effects.  It  has  been  found  that  the  results  obtained  by  applying 
a  constant  current  to  a  nerve  depend  upon  the  direction  in  which 
the  current  flows  through  the  preparation. 

A  current,  for  instance,  which  in  passing  through  the  nerve 
from  the  anode  (positive  electrode)  to  the  kathode  (negative  elec- 
trode) flows  in  the  direction  of  the  muscle,  is  called  a  descending 
current;  while  one  flowing  in  a  direction  away  from  the  muscle, 
is  an  ascending  current.  If  a  current  of  such  strength  is  chosen 
that  the  closing  shocks  only  are  effective,  its  direction  is  of  no  con- 
sequence. This  is  true  also  when  the  current  is  increased  in 
strength,  so  that  both  opening  and  closing  shocks  are  capable  of 
causing  the  muscle  to  contract.  With  a  strong  current,  however, 
it  is  found  that  the  closing  shock  in  an  ascending  current  and  the 
opening  shock  of  a  descending  current  cause  no  contraction.  In 
order  to  understand  these  results,  it  is  necessary  to  consider  the 
changes  that  a  constant  current  produces  in  a  nerve  to  which  it  is 
applied.  These  are  known  as  electrotonic  changes,  and  they  differ 
in  character  at  the  anode  and  the  kathode,  so  that  the  condition 
at  the  former  has  been  named  anelectrotonus,  while  that  at  the 
latter  electrode  is  known  as  katelectrotonus.     While  the  current  is 


NERVE  AND  MUSCLE. 


157 


flowing,  the  irrltahilihi  oft  lie  nmr  is  /v»t'W  at  the  kniluxlr  ami  i.s 
/ofcewV  ut  the  a/(o(/c,  iiiul  this  cuiiditiuii  is  rrrcr.'<r(l  iiimie(halcly 
when  the  current  ceases  to  Jloir.  A  rise  of  irritiihility  and  an  ex- 
citation are  inseparable.  The  underlying  causes  of  i)oth  are  the 
same.  It  may  be  accepted  then  that  the  rise  of  irritability  of  the 
nerve  at  the  kathode  when  the  stimulating  current  is  elose<l,  and 
at  the  anode  when  the  current  is  opened,  indicate  the  generation 
of  nerve-impulses. 

CId.viki  c.rdfofioiis  arise  at  the  kathode,  while  opening  excita- 
tlon><  arise  at  the  anode.     Moreover,  during  c/cctrotoiim  the  co/i- 


FiG.  26. 


Muscle-nrrvc  preparations:  with  the  nerve  exposed  in  ^1  to  a  desfCTifiinf/ and  in 
B  to  an  asrending  constant  current '  Foster).  In  eat-h,  a  is  the  anode,  k  the  Itatliode 
of  the  constant  current;  x  represents  the  spot  where  the  induction-shocks,  used  to 
test  the  irritability  of  the  nerve,  are  sent  in. 

ductivify  is  increased  slightly  at  the  kathode,  and  decreased  greatly 
at  the  anode.  When  the  current  ceases  to  flow,  the  conductivity 
is  greatly  lowered  at  the  kathode  and  is  raised  at  the  anode.  Re- 
flection will  make  clear  that  with  an  ascending  current  the  closing 
contraction  fails  to  apjiear  because  the  conductivity  is  so  lowered 
at  the  region  of  the  anode  that  the  excitation  which  arises  at  the 
kathode  cannot  reach  the  muscle  With  a  descending  current  the 
opening  contraction  fails  to  appear  because  the  comluctivity  is  so 
lowered  at  the  kathode  that  the  nerve-impulse  generated  at  the 


158 


NERVE  AND  MUSCLE. 


anode  cannot  reach  the  muscle.  The  impulses  that  originate  at 
the  electrode  nearest  the  muscle  are  the  only  ones  that  are  effec- 
tive. At  some  point  between  the  electrodes  the  region  of  increased 
irritability  merges  into  that  of  decreased  irritability.  This  point 
is  nearer  the  anode,  but  with  increase  of  strength  of  current  it 
approaches  the  kathode.  The  facts  relating  to  the  effect  of  direc- 
tion of  current  on  the  resulting  contraction  constitute  what  is 
known  as  Pfiuger's  law. 


Current-strength. 

Ascending  current. 

Descending  current. 

"  Make." 

"Break." 

"  Make." 

"  Break." 

Contraction. 
Contraction. 
Contraction. 

Medium  current    .   ^ 

Contraction. 

Contraction. 
Contraction. 

Contraction. 

When  a  nerve  intact  within  the  tissues  of  an  animal  is  sub- 
jected to  an  electrical  current,  it  is  impossible  to  prevent  the 
spread  of  the  latter  through  the  surrounding  tissues.  At  the 
poi7it  of  entrance  of  the  current  it  spreads  out  hrusli-lihe,  to  be 
concentrated  again  at  the  point  of  exit.  Directly  under  the  physi- 
cal anode  the  current  enters  the  nerve,  flows  through  it  at  varying 
angles,  and  so  forms  in  the  nerve  a  physiological  anode  and 
kathode.  The  same  thing  happens  at  the  point  of  exit  of  the  cur- 
rent. Therefore  there  are  four  points  from  which  an  impulse 
may  be  generated.     There  may  be : 

1.  An  anodic  closing  contraciion,  which  is  the  result  of  an  im- 
pulse generated  at  the  physiological  kathode  under  the  physical 
anode. 

2.  An  anodic  opening  contraction,  which  is  the  result  of  a 
change  developed  at  the  physiological  anode  under  the  physical 
anode. 

3.  A  kathodic  closing  contraction,  which  is  the  result  of  an  im- 
pulse generated  at  the  physiological  kathode  under  the  physical 
kathode. 

4.  A  kathodic  opening  contraction,  which  is  the  result  of  an 
impulse  generated  at  the  physiological  anode  under  the  physical 
kathode. 


h'KItVK   ASH   MCSCLK.  1  oO 

These  are  al)l)roviat('(l,  rc'S|M'<-tively,  ACC,  A()('.  KCC,  K()(". 
When  the  stiimihuiiiir  ciirreiit  is  increased  ;.'ra<hially  in  stn'ii|rtii, 
they  appear  in  tlie  Iblhnvini,^  order:  KCC,  ACC,  AOC,  and 
K()C.      This  order  of  appearance  is  ex|)hiined  hy  three  facts  : 

1.  When  the  current  is  closed,  the  impulse  is  jreneraled  at  the 
kathode  ;  and  when  it  is  opened,  at  the  physiolo^'ical  anode. 

2.  The  impulse  developed  at  the  kathode  is  more  effective  than 
the  one  developed  at  the  anode. 

3.  The  etl'ect  of  the  current  is  greatest  where  the  density  is 
greatest. 

When  nerve  and  muscle  are  diseased,  the  ACC  and  KOC  are 
obtained  respectively  with  weaker  currents  than  KCC  and  AOC. 
This  is  known  as  the  reaction  of  dei/eiienition.  It  has  been  found 
that  when  a  current  is  passed  through  a  nerve  or  muscle  at  rir/Itt 
angle/i  to  the  direction  of  its  fibres  it  has  no  stimulating  eflect. 

The  irritability  of  a  preparation  depends  upon  changes  in  its 
environment  and  upon  changes  within  itself.  Chanf/esot'  €)iriro)i- 
mcnt  include  nierJiaiiica/  agencies,  temperature,  chemical  agencies, 
and  electrical  currents.  ^lechanical  agencies  acting  on  living  sub- 
stance usually  first  increase;  but  later  destroy  the  irritability.  In 
general,  C(dd  decreases,  while  heat  increases  the  irritability,  but  in 
this  case  it  is  necessary  to  take  into  consideration  the  character  of 
the  stimulus  employed.  Tissues  differ  normally  in  their  response 
to  various  stimuli.  A  medullated  verve,  for  instance,  responds  better 
to  an  induced  current  than  to  mechanical  or  chemical  stimuli,  but 
the  application  of  cold  makes  it  more  susceptible  to  the  effects  of 
mechanical  stimulation  than  to  the  exceedingly  short  intluced 
current.  Chemicals  first  raise  and  then  lower  the  irritability. 
Dr|irivation  of  tlie  blood-supply  is  equivalent  to  a  change  in  the 
chemical  environment  of  a  tissue.  That  the  normal  irritability  is 
dependent  upon  the  blood-supply  is  shown  by  Stenson's  experiment 
on  the  rabbit,  in  which  the  alxlominal  aorta  was  closed  by  cora- 
pression.  The  paralysis  which  follows  tliis  procedure  is  due  suc- 
ce.<sively  to  the  loss  of  function  of  nerve-cells  in  the  cord,  then  of 
the  motor  end-plates,  and  finally  of  muscle-  and  nerve-fibres. 

That  the  irritability  of  a  preparation  depends  upon  changes  that 
may  take  place  within  itself  is  shown  by  the  sejiaration  of  a  nerve- 
fibre  from  its  cell-body  and  by  the  eH'ects  of  functional  activity. 
The  metabolism  of  a  cell  tlepen(ls  upon  the  presence  of  nuclear 
juatter,  so  that  if  a  nerve-fibre  is  cut  off  from  its  cell-body,  it  will 


160  NERVE  AND  MUSCLE. 

degenerate.  During  this  process  there  are  first  an  increase  and 
then  a  decrease  of  irritability.  A  muscle  separated  from  the  cen- 
tral nervous  system  by  section  of  its  motor  nerve  will  also  degenerate. 
After  a  period  of  two  weeks  or  so,  it  responds  better  to  stimuli  of 
long  duration  than  to  those  of  short  duration,  and  gradually  be- 
comes less  and  less  irritable  to  the  end  of  the  seventh  or  eighth 
month.  Functional  activity  leads  first  to  an  increase  of  irritability, 
but  later  in  this  case  also  to  a  decrease.  This  is  attributable  to 
both  the  consumption  of  its  store  of  nutriment  and  to  the  accumu- 
lation of  waste  products.  Some  physiologists  have  drawn  a 
distinction,  between  the  results  of  these  two  processes.  Waste 
products  if  formed  faster  than  they  can  be  gotten  rid  of,  give  rise 
to  fatigue,  while  the  consumption  of  stored  or  available  nutriment 
gives  rise  to  exhaustion.  That  waste  products  are  formed  during 
activity,  is  shown  by  an  experiment  of  Mosso.  Having  found  the 
injection  of  a  definite  amount  of  blood  from  a  rested  dog  into  the 
veins  of  another  to  be  without  effect,  he  repeated  the  injection  by 
using  the  blood  of  a  dog  completely  tired  out  by  a  hard  day's 
work.  The  dog  receiving  the  blood  showed  all  the  signs  of  extreme 
fatigue. 

It  is  said  that  in  order  that  protoplasm  may  conduct,  it  must  be 
continuous.  A  break  in  the  physiological  continuity  of  protoplasm, 
as  when  a  nerve  is  crushed  at  one  point,  completely  bars  the  con- 
duction process.  The  cut  ends  of  the  nerve  when  placed  in  contact 
will  not  transmit  a  nerve-impulse,  which  distinguishes  the  latter 
from  an  electrical  current,  which  passes  readily  from  one  part  to 
the  other.  A  conduction  process  having  i*eached  the  boundaries 
of  the  cell  in  which  it  has  originated,  may  cause  the  generation  of 
a  similar  process  in  a  contiguous  protoplasmic  mass.  This,  for  in- 
stance, is  shown  by  the  relations  of  the  end-brush  of  one  cell  to 
the  dendrites  of  another.  But  fibres  of  muscles  and  nerves  do 
not  stimulate  their  neighbors  normally  as  they  lie  side  by  side, 
since  their  sheaths  prevent  even  contiguity.  That  the  conduction 
process  passes  in  both  directions  along  the  length  of  the  fibre,  may 
readily  be  seen  in  muscle,  where  it  is  accompanied  by  a  change  of 
form.  In  nerves  it  may  be  demonstrated  by  Kuehne's  experiment 
on  the  sartorius  of  the  frog.  The  end  of  the  muscle  after  being 
slit  longitudinally  for  a  small  distance,  is  stimulated  at  one  tip, 
which  causes  contraction  of  both  tips.  Cross-conduction  between 
muscle-fibres  being  impossible,  the  impulse  generated  in  the  nerve- 


yKRVIC  AND   MUSCLE. 


i(;i 


fibres  of  one  tip  must  pass  hack  to  other  l)raiichc.s  of  the  same 
nerve-tihre,  and  thus  cxciti'  tlie  other  tip.  A  siinihir  experiment 
inav  he  made  on  tlie  eh-etrical  orjjan  of  Maliij>li'niriif<.  The  ante- 
rior roots  of  spinal  nerves  whicii  contain  Hhres  transmittini; 
normally  in  only  one  direction  may  he  shown  to  transmit  also  in 
the  opposite  direction  hy  means  of  the  electrical  change  accom- 
panying a  uerve-im pulse. 

The  rate  of  conduction  varies  in  different  tissues,  and  is  roughly 
related  to  the  function.  In  muscles  all  gradations  are  to  be  found, 
from  the  0.02  to  O.Oo  metre  per  second  of  the  smooth  muscle-tihres 
of  the  rabbit's  ureters,  to  the  10  or  lo  metres  per  second  in  human 
muscles.  The  rate  in  nerves  may  be  put  at  27  metres  per  .second 
iu  frogs  and  35  metres  per  second  in  man.      The  conductiou  process 


Fic. 


Diagram  of  muscle-curve  (Collins  nnd  Rockwelll :  a,  point  of  application  of  current; 
6,  point  of  begiuning  contraction ;  c,  maximum  ;  d,  return  to  normal. 


sweeps  over  irritable  tissue  in  the  form  of  a  wave,  which  in  muscle 
is  about  800  mm.  long,  while  in  nerve  it  is  about  18  mm.  long. 
ConduHion  is  influenced  l)y  the  same  factors  that  affect  ooiifracfi/ifij. 
The  nature  of  the  process  has  not  l>een  determined,  but  must  be 
either  of  phjisical  or  chemical  character.  It  is  intimately  depen- 
dent upon  metaboli.vn,  yet  all  attempts  to  show  its  chemical  nature 
have,  in  nerves,  resulted  negatively. 

The  movements  made  by  striated  muscles  are  too  (juick  to  be 
followed  accuratelv  by  the  eye,  so  that  resource  is  had  to  what  is 
known  as  the  (jnijihic  inetho'I.  The  muscle,  by  means  of  a  mech- 
anism, is  made  to  write  its  contractions  ami  relaxations  on  a  sur- 
face moving  at  a  uniform  rate.  The  entire  arrangenu-nt  constitutes 
a  myogrnph,  and  the  record  thus  obtained  is  a  myoiimm  (Fig.  27). 
The  myogram  of  a  simple  muscle-contraction  consists  of  three 
11— Phys. 


162  •  NERVE  AND  MUSCLE. 

distinct  portions.  Immediately  succeeding  the  stimulation  is  an 
interval  {latent  period)  of  about  y^-^  of  a  second,  during  which 
the  muscle  makes  no  apparent  change.  During  the  next  -^^-^  of 
a  second  the  muscle  shortens,  and  during  the  last  -j^-^  of  a  sec- 
ond it  lengthens  again.  Contraction  and  relaxation  take  place 
at  first  slowly,  then  faster,  and  finally  slowly  again.  The  entire 
time  involved  may  be  put  at  an  average  of  y-^  of  a  second.  The 
time-relations  vary  with  the  nature  of  the  muscle  and  the  con- 
ditions under  which  it  works.  Finer  methods  of  determination 
have  reduced  the  late7it  period  to  a  mechanical  and  an  electrical 
latent  period  of  0.004  and  0.001  seconds,  respectively.  The  latent 
period  of  the  motor  end-plates  is  about  0.002  to  0.003  of  a  second. 
When  the  striated  muscle  of  a  frog  is  submitted  to  a  series  of 
equal  induction  shocks  at  a  regular  rate,  a  series  of  contractions 
are  recorded,  of  which  the  first  four  or  five  fall  in  height,  and 
are  known  as  the  introductory  contractions.  After  this  there  is 
an  increase  in  the  height  regularly  to  a  maximum  which  forms 
the  "treppe"  or  staircase.  Following  this  again,  the  contractions 
lose  in  height  until  they  disappear,  which  is  known  as  fatigue. 
It  is  very  probable  that  the  introductory  contractions  are  caused 
by  polarization  changes  brought  about  by  the  stimulating  current.^ 

It  is  now  assumed  generally  that  the  molecules  of  any  solution 
which  is  a  conductor  of  electricity  are  in  a  state  of  dissociation 
— i.  e.,  the  molecules  are  divided  into  two  or  more  parts,  called 
ions.  Thus  sodium  chloride  in  water  becomes  separated  into  a 
sodium  ion  charged  positively  with  electricity  and  into  a  chlorine 
ion  charged  negatively.  The  passage  of  a  galvanic  current 
through  such  a  solution  is  accomplished  by  means  of  the  ions, 
and  gives  rise  to  electrolytic  phenomena  consisting  of  a  migra- 
tion of  the  positively  charged  ions  or  kations  to  the  negative  pole 
of  the  galvanic  circuit.  In  like  manner  the  negatively  charged 
ions  or  anions  move  toward  the  positive.  This  effect  is  brought 
about  in  any  moist  tissue  that  will  conduct,  and  is  then  said  to  be 
polarized.  The  difference  of  potential  between  the  kations  and 
anions  sets  up  a  current  (polarization  current)  in  a  direction  oppo- 
site to  that  of  the  inducing  current. 

It  happens  thus  that  a  polarization  current  produced  in  any 

1  From  unpublished  experiments  made  in  the  Physiological  Laboratory 
of  the  University  of  Michigan. 


NERVE  AM)   MUSCLE. 


lf)3 


tissue — frofj's  muscle,  lor  instJiucc — will  weaken  the  stinuilating 
current  and  conse(|uently  tlie  cHect  which  the  latter  produces. 
In  a  seriej^  of  stimulations  the  ])olari/.ation  etiects  should  theoret- 
ically hecome  greater  as  the  excitation  |»ro<rresses,  hut  this  is  not 
shown  in  serial  muscular  contractions,  since  the  |)olarizati<»n  effects 
are  disguised  eutirely  by  the  staircase. 

The  daircaae  contrartiouK  result  from  the  fact  that  each  stimu- 
lation occasions  a  heightened  irritability,  so  that  the  succeeding 
stimuli  become  more  cHective.  Fatigue  is  caused  by  the  accu- 
mulation of  waste  products  an<l  to  the  consumption  of  available 
nutriment.  When  the  rate  of  stimulation  is  increased,  the  sep- 
arate muscular  contractions  may  not  come  down  to  the  base-line, 
giving  rise  to  the  phenomena  of  contracture.     This  condition  may 

Fig.  28. 


Serial  contractions  of  j^astroonemius  of  frojr,  showing  double  contracture,  intro- 
ductory contraction,  staircase,  and  fatiKUe.  Two  stimuli  per  second,  niaxinml  in- 
duced current.  Muscle  weighted  with  10  grammes  and  used  three  days  after  pithing 
frog. 


Final  portion  of  curve  A,  showing  cradual  relaxation  due  to  fatigue ;  x,  cessation 

of  stimulation. 


be  explained  by  the  fact  tliat  as  the  muscle  contracts  it  becomes 
fatigueil,  resulting  in  a  prolongation  of  the  relaxation.  A  second 
stimulus  reaches  the  muscle  before  the  contraction  resulting  from 
the  first  is  over.  There  is  a  summation  of  contractions.  Double 
coiitrrtcture.t  are  given  by  muscles  composed  of  two  distinct  kinds 
of  fibres,  which  react  differently  to  the  same  stimulus. 


164  NERVE  AND  MUSCLE. 

The  pale  fibres  react  quickly  and  soon  are  fatigued,  while  the 
dark  fibres  have  greater  endurance.  The  summation  of  contrac- 
tions of  the  pale  fibres  occurs  first  and  quickly  raises  the  base- 
line. As  they  become  fatigued,  the  base-line  gradually  sinks 
until  the  dark  fibres  in  a  similar  manner  raise  it  again.  When 
both  dark  and  pale  fibres  are  fatigued,  separate  contractions,  and 
relaxations  no  longer  take  place,  and  the  base-line  gradually 
sinks.  With  still  more  frequent  rates  of  stimulation  the  staircase 
and  contracture  efi'ects  are  merged  into  one  another,  giving  rise  to 
a  very  great  height  of  contraction.  As  the  curve  is  wavy  or 
unbroken,  it  is  known  as  an  incomplete  or  complete  tetanus. 

Tetanus  is  the  result  of  three  factors  : 

1.  Increase  of  irritability. 

2.  Summation  of  contractions. 

3.  Support  offered  by  contracture. 

All  normal  2)hysiological  contractions  must  be  regarded  as  short 
tetani  and  the  normal  impulse  as  a  discontinuous  form  of  excita- 
tion.    As  the  evidence  of  this  may  be  cited  the  fact  that  muscles 

Fig.  29. 


Curve  of  tetanus.    (Chapman.) 

give  out  a  sound  when  contracting,  implying  that  their  finest  parti- 
cles are  in  a  state  of  vibration.  Wollasten  determined  the  rate  to 
be  from  36  to  40  per  second.  By  means  of  vibrating  reeds  Helm- 
holtz  reduced  the  rate  to  18  to  20  per  second,  which  gives  a  tone 
imperceptible  to  the  ear.  Lately  the  rate  has  been  made  still 
slower,  being  placed  at  an  average  of  about  10  per  second.  Tre- 
mors also  give  evidence  that  voluntary  movements  are  not  contin- 
uous. 


NhliVK  AM)   Ml'SiJLE.  Uio 

The  energy  lil)i'rate«l  In-  imiscle  apjtears  in  inechauical,  thermal, 
autl  eleitr'irnl  form.  Tlif  last  is  so  small  that  in  (|uautitative 
(lett-rmiiiations  it  is  ne;rlij:il)lt'.  ( )iily  oiu'-fourth  to  oiie-tweiitieth 
of  tilt'  c-ht'iuical  eiKTiry  liheratrd  l»y  the  muscle  a|)j)ears  a.s  nie<'haii- 
ifal  eiier}.'y.  The  work  done  hy  a  muscle  (lepenil;?  ujm»ii  its  nature 
and  condition,  the  stimulus  applied,  and  the  mechanical  conditions 
under  which  the  work  is  done.  Work  is  calculated  hy  multiplying 
the  load  into  the  heiirht  to  which  it  is  lifted.  The  ahsolnte  muscular 
force  of  a  muscle  is  the  maximum  weijrht  that  it  can  lift  j>er  unit 
cross-section.  This  for  the  frog  is  3  kilogramnies  |>er  square 
centimeter.  The  heat  liberated  by  active  tissue  is  measured  by  a 
thermopile  or  a  bolometer.  The  first  consists  of  a  certain  number 
of  junctions  of  two  dissimilar  metals  like  antimony  and  bismuth, 
which  develop  an  electrical  current  whenever  any  two  of  the 
junctions  are  at  a  ditfereut  temperature.  The  action  of  a  bolometer 
dejiends  U{X)n  the  fact  that  the  electrical  resistance  of  a  wire  varies 
with  the  temperature.  An  isolated  muscle  has  by  means  of  these 
instruments  been  found  to  produce  by  a  single  contraction  per 
gramme  of  muscle  substance  sufficient  heat  to  raise  3  milligrammes 
of  water  1  degree  centigrade. 

Electrical  energy  is  exhibited  by  many  forms  of  living  matter. 
Whenever  any  portion  of  the  latter  becomes  active  or  in  any  man- 
ner undergoes  katabolic  changes,  a  difference  of  potential  manifests 
itself  in  that  the  active  portion  becomes  negative  to  the  rest.  The 
difference  of  potential  is  generally  small,  requiring  a  sensitive 
galvanometer  or  electrometer  to  measure  it.  but  in  some  electrical 
fishes  becomes  as  high  as  200  volts.  When  a  muscle  or  nerve  is 
intact  and  uninjure<l.  it  gives  no  evidence  of  differences  of  poten- 
tial, and  is  therefore  .^aid  to  be  i.-^o-elecfric ;  but  when  the  ends  are 
cut,  so  as  to  present  two  sections  at  right  angles  to  the  longitudinal 
surface,  it  will  be  found  upon  testing  with  non-polarizable  elec- 
trodes antl  a  suitable  galvanometer  that  the  cut  and  therefore 
dying  ends  are  negative  to  the  uninjured  longitudinal  surface. 

The  current  flows  from  the  injured  tissue  through  the  nuiscle  or 
nerve  to  the  electrode  on  the  longitutlinal  surface,  thence  through 
the  galvanometer  back  to  the  starting-point.  Poiius  ecjuidistant 
from  the  centre  on  the  cros.*-section  and  from  the  e«|uator  on  the 
longitudinal  surface  are  at  the  same  potential.  A  current  obtaine«l 
by  mutilation  of  the  tissue  is  known  as  a  current  of  injury,  of  re.'<t, 
or  of  demarcation.     In  a  cat's  nerve  it  has  been  found  to  equal 


166 


NERVE  AND  MUSCLE. 


0.01  and  in  an  ape's  nerve  0.005  of  a  Daniell  cell.     Dead  tissue 
gives  no  current 

It  has  been  found  that  when  living  tissue  is  stimulated,  the 
activity  accompanied  by  katabolic  changes  sweeps  over  it  in  the 
form  of  a  wave.  As  the  latter,  in  muscle  or  nerve,  passes  by  the 
electrodes  it  brings  about  differences  of  potential  which  are  indi- 
cated by  a  galvanometer.     These  differences  of  potential  give  rise 


Fig.  30. 


>*— €^ 


Diagram  illustrating  the  electric  currents  of  nerve  and  muscle :  being  purely 
diagrammatic,  it  may  serve  for  a  piece  either  of  nerve  or  of  muscle,  except  that  the 
currents  at  the  transverse  section  cannot  be  shown  in  a  nerve.  The  arrows  show 
the  direction  of  the  current  through  the  galvanometer  (Foster) :  ab,  the  equator. 
The  strongest  currents  are  those  shown  by  the  dark  lines,  as  from  a,  at  equator,  to  x 
or  to  y  a:  the  cut  enris.  The  current  froni  a  to  c  is  weaker  than  from  a  to  y,  though 
both,  as  shown  by  the  arrows,  have  the  same  direction.  A  current  is  shown  from  e, 
which  is  near  the  equator,  to/,  which  i>;  further  from  the  equator.  The  current  (in 
muscle)  from  a  point  in  the  circumference  to  a  point  nearer  the  centre  of  the  trans- 
verse section  is  shown  at  gh.  From  a  to  6,  or  from  z  to  y,  there  is  no  current,  as  indi- 
cated by  the  dotted  lines. 


to  currents  of  action.  When  a  current  of  action  is  superimposed 
upon  a  current  of  rest,  the  needle  of  the  galvanometer  having  been 
deflected  to  a  certain  extent  by  the  latter,  is  made  to  move  back 
toward  the  zero  point,  giving  rise  to  a  negative  variation.  When 
the  nerve  of  one  (A)  of  two  nerve-muscle  preparations  is  laid 
lengthwise  over  the  muscle  of  the  other  preparation  (B),  and 
the  nerve  of  B  is  stimulated  with  an  interrupted  current,  both 
muscles  are  thrown  into  tetanus.     That  this  phenomenon  is  not 


yEIil'E  AM>   MC6CLE.  167 

due  to  a  spread  of  the  exciting  current  throuirh  the  prepara- 
tions i:?  ^howu  by  ligatiui:  the  uer\-e  of  B  Wiween  the  electrodes 
and  the  nmst-le,  when  all  c«jntra<-tion*  cease.  As  a  matter  of  fact, 
the  muscle-tihres  of  B  jrive  rise  to  currents  of  action  that  are  cir- 
cuited through  the  fibres?  of  nerve  resting  on  it*  surface.  The 
ner\-e-fibre:s  of  A  are  thus  stimulated  and  cause  the  muscle  to 
contract.  Thii  phenomenon  m  known  ws  secondary  tetanua.  As 
the  wave  of  a  nerve-impulse  sweejis  by  the  electrodes,  it  changes 
the  potential  successively  of  one  and  then  of  the  other,  so  that  the 
needle  of  the  galvanometer  is  dedei."te«l  at  one  instant  in  a  positive 
direction  and  in  the  next  in  a  negative  direction.  Currents  of 
action  are  therefore  dipha-nc.  Changes  of  irritability  due  to  the 
passage  of  a  constant  current  have  been  alluded  to  under  electro- 
tonic  changes.  There  are  to  be  observed  at  the  same  time  varia- 
tions in  the  electrical  currents  of  the  nerve  itself — ».  e.,  variations 
in  the  currents  of  rest.  The  constant  current  causes  in  the  nerve 
outside  of  the  electrodes  the  appearance  of  another  current  that 
has  the  same  direction  as  itself,  and  is  called  the  electrotonie  cur- 
rent. The  electrotonie  current  adds  to  or  takes  away  firom  the 
currents  of  rest  acconiing  as  they  are  dowing  in  the  same  direction 
or  in  an  opposite  direction.  The  strength  of  the  electrotonie  cur- 
rent is  dependent  upon  the  strength  of  the  polarizing  current,  the 
length  of  the  region  between  the  electrodes,  and  the  condition  of 
the  nerve.  A  dead  nerre  does  not  manifest  electrotonie  currents, 
and  they  may  be  stopped  by  a  ligature  or  by  crushing  the  nerve. 
Whenever  a  muscle  dies,  it  undergoes  a  change  manifesting 
itself  in  a  loss  of  translucency,  of  extensibility  and  ela-iticity,  by 
the  development  of  a  gradual  contraction,  of  increased  heat-pro- 
duction and  acidity.  This  change  is  called  rigor  morti-i.  It 
usually  affects  the  bo<iy  in  regular  order,  the  jaiCy  neck,  trunk, 
ann.<,  and  leg-i  being  intiuenced  one  after  the  other.  In  general, 
the  more  active  the  protopla.*m  the  sooner  does  it  pass  into  rigor. 
During  life  the  central  nervous  system  is  continually  sending  im- 
pulses to  the  muscles,  keeping  them  in  a  slight  state  of  tension 
called  niuacle-tonus.  If  the  muscles  are  severed  from  the  central 
nervous  system  by  curare,  the  development  of  rigor  is  delayed. 
Cold  delays  and  warmth  i  38°  to  40°  C. )  favors  rigor.  The  caujte 
of  rigor  is  the  cxtgnlation  of  the  semijiuid  mu-*cle-*iib<tanee.  Mus- 
cle-plasma which  can  be  expressed  from  frozen  musc-le  tx)niains 
two  proteids,  paramyosinogen  and  myosinogen.     By  the  action  of 


168  NERVE  AND  MUSCLE. 

a  myosin  fermeiit  they  are  converted  into  myosin.  Rigor  caloris 
is  caused  by  the  precipitation  of  various  proteids  of  the  muscle  by 
heat. 

QUESTIONS  ON  CHAPTER  XI. 

What  properties  characterize  muscle  and  nerve  ? 

What  properties  have  they  in  common  ? 

Which  ones  have  they  entirely  lost? 

What  is  a  nerve-muscle  preparation  ? 

Give  proofs  that  muscle  is  irritable  independently  of  nerves. 

Define  a  stimulus.     How  many  classes  are  there  ? 

Upon  what  factors  do  the  results  of  stimulation  depend? 

Why  is  an  electrical  stimulus  usually  a  desirable  one? 

Distinguish  between  voltaic  and  induced  currents. 

Define  opening  and  closing  shocks.     Which  is  the  stronger? 

Tell  why  the  breaking  induced  current  is  stronger  than  the  making. 

What  are  subminimal  and  supermasimal  stimuli  ? 

What  changes  take  place  in  the  contraction  of  a  muscle  as  the  excitation 
increases  in  strength? 

What  is  Du  Bois-Eeymond's  law? 

Illustrate  how  density  of  current  affects  its  exciting  power. 

Discuss  the  results  of  duration  of  stimulus. 

What  are  ascending  and  descending  currents? 

Discuss  changes  in  irritability  and  conductivity  of  a  nerve  during  electro- 
tonus. 

What  are  anelectrotouus  and  katelectrotonus  ? 

What  is  the  relation  of  rise  of  irritability  to  excitation? 

Discuss  in  detail  Pfliiger's  law. 

At  what  points  may  an  impulse  be  generated  when  a  nerve  in  situ  is  sub- 
jected to  a  constant  current? 

In  what  order  do  the  contractions  occur  as  the  strength  of  current  is  in- 
creased ?    Give  reasons. 

What  is  meant  by  the  "reaction  of  degeneration  ?" 

Upon  what  factors  does  the  irritability  of  a  preparation  depend? 

Discuss  the  effect  of  changes  in  environment  upon  the  irritability  of 
tissue. 

Discuss  the  effect  of  severing  a  nerve-fibre  from  its  cell-body. 

How  does  functional  activity  alter  irritability  ? 

Distinguish  between  fatigue  and  exhaustion. 

Give  proof  that  waste  products  are  formed  during  activity. 

What  distinguishes  between  an  electrical  current  and  a  nerve-impulse? 

Give  proof  that  conduction  may  pass  in  all  directions  in  protoplasm. 

Give  rates  of  conduction  in  various  tissues. 

What  factors  affect  conductivity  ? 

What  are  the  lengths  of  the  conduction-waves  in  muscle  and  nerve? 

By  what  method  are  muscle-movements  studied  ? 

Describe  a  simple  myogram. 

What  is  the  latent  period  of  the  motor  end-plates? 

Discuss  the  introductory  contractions,  staircase  contractions,  and  fatigue. 

What  is  the  cause  of  contracture? 

What  factors  cause  tetanus? 

What  is  the  nature  of  voluntary  contractions? 

Discuss  the  reasons  for  thinking  voluntary  contractions  tetani. 


QUKSTFONS  ON  CHAPTER  XI.  Ki'J 

How  is  the  chemical  eiiiTKy  of  imiscic  lihiratod? 

What  i)riii)i)rli()ii  ajipoars  as  incchaiiical  t-iuTnyV 

Upon  what  factors  (Iocs  the  work  of  a  muscle  (lepnn<l? 

How  is  Work  estimated? 

What  is  al)soliitc  miisciilar  force?     Give  its  value  in  frog's  niusdo. 

How  is  the  lieat  liherated  hy  tissue  measured? 

How  is  the  electricity  liherated  by  tissue  measured? 

NVlicii  are  muscles  isoelectric? 

What  is  a  eiirreiil  of  rest?     Trace  its  path. 

What  are  currents  of  action? 

What  causes  a  m'fj;ativo  variation? 

Kxplain  secondary  tetanus. 

Explain  why  a  current  of  action  is  diphasic. 

Discuss  electrotouic  currents. 

How  docs  ri.u:or  mortis  manifest  itself? 

In  wliat  order  doi's  it  atl'cct  the  various  portions  of  the  body? 

What  is  the  cause  of  rigor  mortis? 

What  is  the  cause  of  rigor  cahu-is? 

What  factors  influence  the  onset  of  rigor? 

What  is  muscle-tonus,  and  to  what  is  it  due? 


CHAPTER  XII. 

CENTRAL  NERVOUS  SYSTEM. 

The  entire  nervous  system,  for  the  sake  of  convenience,  is 
divided  into  a  number  of  parts  : 

1,  The  central  nervoii!<  xij-'<tein  or  the  cerebrospinal  axi.s  (brain 
and  spinal  cord). 

2.  The  peripheral  nervous  si/dem  (spinal  and  cranial  nerves 
and  ganglia,  sympathetic  ganglia  and  nerves).  Physiologically 
considered,  such  a  division  of  the  nervous  system  has  no  partic- 
ular significance ;  the  functions  of  these  part*;  are  intimately 
related  and  dependent  upon  one  anotlier,  and  form  such  an  indi- 
visible iHiit  that  any  detached  group  of  nervous  .structures  woidd 
have  no  meaning.  The  essential  constituents  of  the  nervous  sys- 
tem are  separate  but  cont'ujnous  nerre-celU  or  neurones.  A  neurone 
is  meant  to  include  every  part  of  a  nerve-cell  under  the  control 
of  a  given  nucleus.  It  consists  of  the  cell-bodi/  and  all  its  out- 
groivths.  Of  the  latter,  the  axones  are  of  various  lengths  ;  some 
in  man  spanning  almost  the  entire  length  of  the  body.  The  ends 
of  the  axones  and  of  the  branches  which  an  axoiic  gives  off 
along   its  length  are  divided  into  tine  twigs  or  trrniinal  arboriza- 


170 


CENTRAL  NERVOUS  SYSTEM. 


tions. 


Fig.  31. 


The  remaining  branches  of  the  nerve-cell  do  not  attain 

the  length  of  the  axone,  but 
very  soon  divide  dichotom- 
ously,  so  that  they  also  form 
finely  divided  terminal  arbo- 
rizations. The  arrangement 
of  neurones  is  such  that  the 
end-brush  of  the  axone  of 
one  cell  is  in  intimate  rela- 
iton  to  the  end-brushes  of 
the  dendrite  of  another  cell. 
Therefore  an  impulse  gener- 
ated in  any  one  neurone  is 
transmitted  to  its  neighbor, 
which  in  turn  passes  it  on  to 
the  next  neurone.  It  must 
be  understood,  of  course,  that 
it  is  not  the  impulse  that  is 
transmitted,  but  that  an  im- 
j)ulse  reaching  the  end-brush 
of  one  axone  has  the  jwwer  to 
generate  another  impulse  in 
the  dendrites  of  the  contig- 
uous neurone.  The  general 
plan  of  a  nerve-cell  and  its 
prolongations  is  shown  in 
Fig.  31. 

It  is  the  function  of  the 
nervous  system  to  bring  the 
body  into  relation  with 
changes  in  its  environment 
and  to  preserve  the  harmo- 
nious working  of  all  its  or- 
gans.    All    parts   of  an    or- 


/m^ 


Fig.  31.— Neurone  with  long  axone 
proceeding  as  the  axis-cylinder  of  a 
nerve-fibre:    n  c,  nerve-cell   proper; 

d,  dendrites  ;  x,  axon  ;  d  g,  dendrite 
showing  gemmulae  \  a  d  g,  apical  den- 
drite with  gemmulse  ;  c,  collaterals  ; 

e,  end-tufts,  pyramidal  cell  of  the 
cerebral  cortex.   (S.  Rain6n  y  Cajal.) 


CKSTIIM.   SKRVorS  SYSTEM. 


171 


gaiiisni  ari',  lluTct'orc,  hound  to^^fctlii-r 
the  cerel)r()S[iiiial  axis  llu-  axoiies 
of  nerve-eells,  calh-d  ncrvc-liljres, 
pa*!S  to  all  portions  of  the  Ixxly. 
Tbey  do  not  pass  out  indiscrimi- 
nately, hut  aiv  groupi'd  to^a-ther 
into  nervo-trunks  to  form  flic  cni- 
)il(i/,  f<iiiii(i/,  and  .•<i/iiip(tflit'lic  m/sfonn, 
as  is  indicated  in  Fi<,^s.  .'>2,  .'58,  and 
84. 

Neurones  whose  tihres  hcgin  in 
sensory  structures  in  the  skiu,  mus- 
cles, or  tendons,  carry  impulses  into 
the  central  nervous  system,  and  are 
known  as  afferoit  neurones.  Those 
whose  iihres  carry  impulses  from  the 
central  system  to  the  structures  which 
the  central  nervous  system  controls 
are  known  as  efferent  fibres. 

Fig.  "t}.— T'nder  surfiice  or  base  of  the  cere- 
brum and  cerehelhini,  and  of  the  pons  Varolii 
and  medulla  oblongata,  also  the  anterior  sur- 
face of  the  spinal  cord.  Id  show  the  mode  of 
orifrin  of  the  spiiial  nerves  fmui  the  spinal 
cord,  and  the  cranial  nerves  fmni  the  base  of 
the  brain:  a, a.  cerebral  hemispheres  :  h,  rifilit 
half  of  cerebellum:  m,  medulla  obliin<,'at!i ; 
above  this  is  a  transverse  white  mass,  the  pons 
Varolii;  r,  C,  the  spinal  cord,  showing;  its  cer- 
vical and  himbar  enlargements,  and  its  pointed 
terminations;  f,  the  caiida  e(iuina,  formed  by 
the  elongated  roots  <if  the  lumbar  and  sacral 
nerves  ;  1  to  9,  the  several  cratiial  nerves  aris- 
ingr  from  the  base  nf  the  brain  and  the  sides  of 
tlie  medulla  oblonjsfata.  Below  these,  on  each 
side,  are  the  mots  or  origins  of  the  spinal 
nerves,  cervical,  dorsal,  lumbar,  and  sacral. 
In  some  of  these  the  double  root  can  be  seen, 
and  the  swellinfr  or  panglion  on  the  posterior 
root;  n,  x,  the  axillary  or  brachial  plexus, 
formed  l>y  the  four  lower  cervical  and  lirst 
dorsal  spinal  nerves;  /,  tlii'  lumbar  plexus;  .<, 
the  sacral  ]>Kxns,  formed  by  the  last  lumtiar 
nerve  and  first  four  sacral  nerves:  t  sliows  a 
piece  of  the  sheath  of  the  conl  cut  open,  and 
with  it  a  portion  f)f  the  ligamenium  deiilicu- 
laHim  which  s\i)>ports  the  cord;  .1,  a  trans- 
verse section  tbrouirli  the  conl,  to  show  the 
form  of  the  gray  cornua  or  horns,  in  the  midst 
of  the  white  substance,  li  shows  the  sanu- 
parts,  and  also  the  membrane  of  the  cord  ;  an<l 
the  anterior  and  posterior  roots  of  a  pair  of 
spinal  nerves  springing  from  its  sides. 


hy  norvc-structurcs.      from 
Fi...  :,-L 


Fig.  33. 


CENTUM.    MlliVOUS  FiYSTEM.  17.". 

Ill  :i<l«liti(Hi,  llu'iT  ixw  cclLs  w  liosc  liraiiclKS  do  not  Icavf  (hi- 
eeiitial  lu  rvous  system,  and  whosi*  fundi  )n  it  is  to  <"onvi'y  impulses 
from  one  portion  of  tlie  (•iTel)rospinal  axis  to  aiiotlnr.  Tliese 
are  ceiitni/  neurones. 

A  rrficr  act  ( Fi.^.  .'io)  is  the  simplest  roarduinltil  miction 
whieli  may  take  place,  and  not  necessarily  involve  coiixcionxttem, 
as  may  he  easily  demonstrateil  in  the  froi^.  If  the  hrain  of  tins 
animal  is  completely  destroyed,  there  results  at  first  a  state  of 
collai)se,  w  liich  is  known  as  shock,  and  which  in  time  passes  off. 
The  removal  or  injury  of  any  considerahle  mass  of-  nervous  mat- 
ter affects  the  activity  not  only  of  the  part  operated  u|)on,  hut 
also  of  distant  structures.  The  nature  of  shock  is  not  well 
known,  but  it  may  he  ex})Iained  as  the  result  of  a  potent 
stimulus  which  throui^h  inhlhifiofi  and  crhaustion  (lepresses  the 
normal  fnnciions.  After  the  froji;  has  recovered  from  the  shock 
it  ai)pears  normal,  with  the  exception  that  it  is  unable  to  hold 
itself  up  with  its  front  limbs,  so  that  the  nose  touches  the  surface 
of  support.  When  the  frog  is  suspended  by  the  lower  lip,  it 
hangs  with  body  and  limbs  in  a  relaxed  condition.  A  stimulus 
api^lied  to  the  skin  of  the  leg  is  followed  by  vigorous  muscular 
responses,  which  seem  to  be  purposeful,  inasmuch  as  the  reaction 
tends  to  remove  the  irritant.  The  essentud  nervous  portions  of 
such  a  preparation  are :  1.  Afferent  fibres  which  arise  in  sense- 
organs  in  the  skin,  muscles,  and  tendons  ;  and  enter  the  s})inal 
cord  by  way  of  the  posterior  roots,  perhaps  stretching  its  entire 
length  and  by  means  of  collaterals  making  wide  connections ; 
2.  The  spinal  cord  with  numerous  central  cells  interpolated  be- 
tween the  terminals  of  the  afferent  and  efferent  fi]>res  ;  3.  The 
efferent  fibres  leaving  by  way  of  the  ventral  roots  and  passing  to 
the  muscles  or  to  the  ganglia  of  the  sympathetic  system. 

The  sensory  stimuli  that  are  received  pass  up   the  nerve-trunks 

Fin.  !W.— Scheme  of  the  nerves  of  a  sopment  of  the  spinnl  cord  (Foster) :  Or.  srray  : 
H',  white  matter  of  spinal  cord:  .1,  anterior;  /*,  posterior  rfiot :  (?,  panelion  on  the 
posterior  root;  .V,  whole  nerve;  .V,  spinal  nerve  proper,  endinp  in  .V,  skeletal  or 
somatic  mnsclc;  .s',  somatic  sensory  cell  or  surface:  A',  in  other  ways;  r,  visceral 
nerve  i  white  ramtis  comnuiiiicansrpassin<r  to  a  tranijlii'n  of  the  synipiithetic  chain  2. 
and  passinpon  as  I''  to  supply  the  more  distant  panvrlion  o-,  then  as  I"  to  the  periph- 
eral panglion  <r'  and  endin?  in  m,  s]ilnnchnic  muscle  :  .<.  splanchnic  sensory  cell  or 
surface:  j,  other  possible  splanchnic  cndinjrs.  From  ii  is  piven  otV  the  revehent 
nerve  r.v.  (gray  ramus  ciuiimiinicansK  which  partly  i^asses  backward  tf)ward  the 
spinal  cord,  and  partly  runs  as  r.  i/i.  in  <'iinnection  with  the  sinnal  nerve,  to  supply 
vasomotor  fconstrictoV)  lihres  to  the  nuiscles  (m)  of  bloodvessels  in  certain  parts, 
for  example,  in  the  limbs;  St/,  the  sympathetic  chain  unitinR  the  panplia  of  the 
series  2.    The  tcruiinalions  of'  the  otlier  nerves  arising  from  2,  <r,  o-',  are  not  shuwu. 


174 


CENTRAL  NERVOUS  SYSTEM. 
Fig.  34. 


Ganglia  and  nerves  of  the  sympathetic  system.     (Daltou.) 

to  the  posterior  nerve-roots,  and  thus  to  the  spinal  cord.     In  the 
cord  the  impulse  may  be  sent  to  the  brain,  producing  consciousness, 


CKSTRAL    MiRVors  SYSTh'M. 


175 


etc.;  or  else  the  hnpn/xr  in  the  cord  nmy  ho  transniitteil  directly  to 
sonic  inolnr  cell  in  tha  (iiitt'ilor  liDni,  .stirrinjj^  it  to  activity,  with  the 
result  that  there  is  iiiiisrii/(ir  action.  A  person,  lor  example,  may 
he  tickK'd  witii  a  leather,  and  the  suhject  brushes  away  the  olienil- 
ini;  ()l)ji'ct  either  with  or  without  consciousness  of  what  he  is  doin^. 
It"  he  tloes  it  iinconxcioKxlii,  the  rrficx  act  takes 
place  in  the  cord  ;  if  he  brushes  away  the 
feather  as  a  result  of  the  imj)rei^iiiun  received 
in  his  brain,  the  rejiex  act  took  place  in  the 
bniiii.  Furthermore,  a  person  may  perform 
a  rellex  act  throuiijh  the  rejiex  ventres  in  the 
cord,  and  yet  after  the  act  is  completed  he 
may  receive  the  sensory  impulse  in  the  brain. 
Such  an  act  may  be  simple  and  involve  a 
sintjle  muscle,  or  complex  and  involve  many  ; 
thus,  a  ray  of  litjht  falling  upon  the  retina 
causes  a  simple  reflex  contraction  of  a  single 
muscle,  and  the  iris  contracts.  As  an  illus- 
tration of  a  complex  reflex  action,  however, 
irritation  of  the  lari/nx  causes  not  only  a  closing  of  the  (jloftis,  but 
also  a  contraction  of  all  the  muscles  involved  in  forced  expiration 
or  coacfhimj.  The  spinal  cord  in  man  is  so  much  under  the  con- 
trol of  the  higher  centres  that  its  capabilities  for  reflex  action  are 
often  cvsrlooked.     After  injury  to  the  spinal  cord  the  I'etlex  acts 


iJiatrram  illustrating 
siniplt-'St  form  of  reflex 
apparatus.     (I-'oster.) 


Fig.  sr,. 


Transverse  section  of  the  spinal  cord :  n.  b,  spinal  nerves  of  tlie  rifjlit  and  left 
sides;  '/,  oriijin  r)f  the  anterior  root;  e,  origin  of  the  posterior  root;  r,  panglion  of 
the  posterior  root. 


are  apt  to  be  purposeless  and  fruitless.  In  many  lower  animals 
retlex  action.^,  after  the  cord  has  been  divided,  are  extensive  and 
well  coordinated.  This  is  well  marked  in  the  frog.  Yet  the  dif- 
ference is  one  of  degree  only.  Jn  man  manji  nets  are  accom])li.ilu'(l 
as  reflex  movements  occurring  in  the  cord,  although  it  is  incapable 
of  initiating  them  itself. 


176  CENTRAL  NERVOUS  SYSTEM. 

Stimulation  of  afferent  fibres  brings  about  a  response,  usually, 
of  those  muscles  innervated  from  the  same  segment  of  the  cord,  but 
the  reflex  may  involve  corresponding  muscles  of  the  other  side  of 
the  body  or  muscles  innervated  from  segments  of  a  lower  or  higher 
level.  It  may  be  accepted  as  a  general  rule,  that  an  afferent  im- 
pulse when  it  passes  through  the  cord  tends  to  die  out,  and  that  it 
reaches  more  cells  than  actually  are  discharged.  Further,  that 
the  pathway  taken  by  an  impulse  is  but  one  of  many  possible 
paths.  Reflex  acts,  like  all  others,  involve  time.  It  has  been 
found  that  the  latent  period  varies  from  0.05  to  0.40  of  a  second. 
It  is  decreased  as  the  strength  of  the  stimulus  is  increased.  With 
electrical  or  mechanical  stimuli  the  response  often  occurs  only  after 
a  given  number  of  stimuli  have  been  applied.  In  such  cases  there 
is  a  summation  of  the  effects  of  the  stimuli  in  certain  parts  of  the 
reflex  chain.  It  has  been  found  that  three  segments  only  are 
necessary  in  the  frog  to  produce  the  reflex  clasping  movement  that 
the  male  develops  during  the  breeding  season.  The  higher  the 
animal  stands  in  the  scale  of  development,  the  more  complicated 
does  the  structure  of  the  cord  become,  but  the  less  are  the  seg- 
ments capable  of  acting  independently.  Most  of  the  reflexes  oj 
man  are  those  that  involve  unstriped  musele  or  glands.  These  and 
others  are  :  deglutition,  peristalsis  of  the  intestine,  defecation,  mic- 
turition, emission,  vaginal  peristalsis,  parturition,  coughing,  sneez- 
ing, the  tendon-reflexes,  the  reactions  of  the  vascular  system,  and 
the  action  of  glands.  Many  reflexes  which  in  the  young  are  un- 
controlled are  later  brought  under  the  action  of  the  will.  This  is 
due  probably  to  the  growth  of  fibres  from  the  brain  into  the  cord, 
or  rather  to  more  perfections  made  by  such  fibres. 

The  spread  of  impulses  from  one  to  many  neurones,  which  is 
termed  diffusion,  differs  somewhat  along  afferent  and  efferent  paths. 
Diffusion  of  afferent  impulses  does  not  take  place  until  they  have 
reached  the  cord,  while  diffusion  of  efferent  impulses  takes  place 
in  the  peripheral  ganglia.  Fibres  passing  from  the  cord  to  the 
sympathetic  ganglia  are  termed  p>reganglionic  fibres,  while  those 
passing  from  the  ganglia  to  the  peripheral  structures  are  termed 
postganglionic  flhres.  It  is  found  that  each  preganglionic  fibre  is 
distributed  to  more  than  one  cell  in  the  ganglion,  so  that  an  im- 
pulse passes  out  of  the  ganglion  over  a  number  of  paths. 

Normally,  impulses  are  always  coming  into  the  cord  from  all 
parts  of  the  body  ;  are  diff'used  throughout  the  centrrJ  nervous 


CENTRAL  MiJiVurS  SYSTEM. 


17' 


system  to  a  jjreater  or  less  extent  ;  and  are  the  cause  of  efrerent 
impulses  that  (•(intiiuially  are  leaviiiL''  the  cord  to  he  transmitted  to 
the  various  strudnrr.s  of  the  liodv,  kecpinir  them  in  a  stafr  of  tone. 
This  is  uoticeal)le   in   many  patli()h)gieal   cases,   especially   iti  the 


Kk!.  :i7. 


Facial  paralysis  of  the  right  side.    (Dalton.) 

insane,  where  phases  of  mental  exaltation  and  depression  are  de- 
picted in  the  expression  of  the  face,  so  that  they  appear  like  (lifer- 
ent persons.  The  leirs  of  a  pithed  frog  do  not  liany-  in  a  perfectly 
relaxed  position  unless  the  sciatic  nerve  is  severed.     Kigor  mortis 

12— Phys. 


178  CENTRAL  NERVOUS  SYSTEM. 

usually  sets  in,  in  both  legs  of  the  frog  at  the  same  time,  but  when 
the  sciatic  nerve  of  one  limb  is  cut  immediately  after  the  killing 
rigor  mortis  is  delayed  in  that  leg.  This  is  accounted  for  by  the 
fact  that  the  impulses  from  the  cord  hasten  the  onset  of  rigor 
mortis. 

Spinal  reflexes  are  more  or  less  modified  by  impulses  coming 
from  the  brain  or  from  other  sources.  This  is  shown  by  Exner's 
experiment,  in  which  a  rabbit  was  prepared  in  such  a  way  that  an 
electrical  stimulus  could  be  applied  either  to  the  cerebral  cortex  or 
to  the  skin  of  the  foot,  both  being  followed  by  the  same  muscular 
response.  Excitation,  simultaneously,  of  both  places  gave  a  pro- 
portionally greater  response  than  excitation  of  either  alone.  If 
the  skin  was  so  weakened  that  a  muscular  response  did  not  follow 
when  applied  alone,  it  could  be  made  effective  by  stimulating  the 
cerebral  cortex  0.6  of  a  second  previously.  Excitation  of  the 
cortex  had  the  effect  of  making  the  nerve-cells  involved  more  irri- 
table, so  that  they  were  able  to  respond  to  a  weaker  stimulus.  The 
increase  of  irritability  passed  away  in  three  seconds.  It  has  been 
shown  that  the  patellar  tendon-reflex  could  be  reinforced  by  a  vol- 
untary contraction  or  by  a  sensory  stimulation  if  the  interval 
between  them  was  less  than  0.4  of  a  second.  As  the  interval 
became  greater  than  0.4  of  a  second,  the  knee-jerk  was  diminished 
or  inhibited  until  the  time-difference  was  1.7  seconds,  after  which 
the  two  phenomena  ceased  to  influence  each  other.  A  simple 
method  of  showing  inhibition  of  reflexes  is  to  dip  the  toe  of  a 
pithed  frog  into  dilute  acid.  A  contraction  results.  If  the  exper- 
iment is  now  repeated  while  at  the  same  time  the  other  toe  is 
pinched,  it  will  be  found  that  the  latent  period  of  the  reflex  is 
greatly  prolonged,  or  that  no  contraction  at  all  follows.  It  has 
been  shown  that  stimulation  of  the  cortical  areas  for  the  flexors  of 
the  arms  simultaneously  gives  rise  to  an  inhibition  of  the  exten- 
sors, and  that  when  the  extensors  are  brought  into  action  there 
is  an  inhibition  of  the  flexors. 

Voluntary  responses  differ  from  reflexes  in  that  they  are  less 
predictable,  more  variable,  and  that  instead  of  following  in  a  very 
short  interval  they  may  be  delayed  for  a  long  while — possibly 
for  years.  The  most  complex  voluntary  reactions  involve  the 
entire  central  nervous  system,  and  especially  the  cerebral  cortex. 
The  path  taken  by  the  impulse  is  longer  and  involves  more 
neurones,  so  that  in  its  course  it  may  become  much  more  modified. 


CESTnAL  SERVOrs  SYSTEM. 


179 


Impulses  over  afFcrcnt   fibres  pas.s  aloiiir  the  posterior  spinal 
nerve-rootd  aud  euter  the  curii.     Their  path  is  then  aloug  Hhreti 


Fi(i.  ;j8. 


Diagram  showing  pathway  of  the  sensory  impulses :  on  the  left  side  S  ^  represent 
afTerent  spinal  nerve-fibres ;  C.  an  afferent  cranial  nerve-fibre.  These  fibres  terminaie 
near  central  cells,  the  neurone  ."<  of  which  crosses  the  middle  line  and  ends  in  the 
opposite  hemisphere.    (Van  Gehuchten.) 

that  ascend  the  posterior  columns,  and  may  be  either  alone:  a 
short-path  or  a  lontj-path  fibre.  If  it  is  the  htfrr,  they  are  carried 
to  the  dorsal  funiculi,  to  terminate  about  cells  in  the  nuclei  of  the 


180 


CENTRAL  NERVOUS  SYSTEM. 


gracilus  and  cuneatus.  Here  the  impulse  is  taken  up  by  a  second 
set  of  neurones,  which  decussate,  and  then  go  forward  in  the  medial 
lemniscus,  to  end  either  in  the  ventral  portion  of  the  thalamus  or 
in  the  cerebral  cortex.  From  the  thalamus  the  impulse  may  pass 
along  a  third  set  of  neurones  to  the  cortex.  Cranial  afferent 
nerves,  which  are  not  of  special  sensation,  like  those  of  the  fifth, 
the  vestibular  portion  of  the  eighth,  ninth,  and  tenth,  have  a  sim- 
ilar course.  Impulses  taking  short-path  fibres  pass  largely  to  cells 
in  the  dorsal  cornu  of  the  cord,  many  passing  by  way  of  the  col- 
laterals. Cells  of  the  dorsal  gray  horn  send  their  axones  across 
the  cord  to  the  lateral  columns  of  the  opposite  side  and  pass  to  the 
thalamus  through  the  medial  lemniscus. 


Fig.  39. 


Degeneration  of  spinal  nerves  and  nerve-roots  after  section  (Dalton) :  a,  anterior 
root ;  p,  posterior  root ;  g,  ganglion  ;  A,  section  of  nerve-trunk  beyond  the  ganglion ; 
B,  section  of  anterior  root ;  C,  section  of  posterior  root ;  D,  excision  of  ganglion. 

Pathways  or  tracts  of  the  cord  may  be  studied  by  means  of 
degenerations.  A  nerve-fibre  will  degenerate  when  by  section  it  is 
removed  from  the  cell-body  that  governs  its  nutrition. 

If  the  dorsal  roots  are  sectioned  between  the  posterior  root- 
ganglion  and  the  cord,  the  resulting  degeneration  will  extend  down 
the  dorsal  columns  for  two  or  three  centimetres,  and  up  to  the 
nuclei  in  the  dorsal  columns  of  the  bulb  mainly  on  the  same  side 
as  the  section.  On  passing  upward,  however,  the  area  of  degen- 
eration constantly  becomes  less,  owing  to  the  fact  that  fibres  con- 
tinually are  leaving  the  posterior  columns  and  passing  into  the 
gray  matter  of  the  cord.  When  the  cord  is  hemisected,  the  ascend- 
ing fibres  that  degenerate  are  in  the  dorsal  columns,  in  the  dorso- 
lateral  ascending   tract,    and    in    the    ventrolateral    descending- 


CENTRAL   M:ii\'()l'S  SYSTEM.  IHI 

aHceudlng  tract.  Most  of  the  (IcirciicratcMl  lilires  arc  to  ho  found 
on  the  same  side  as  tlie  section,  nltliou^zli  a  few  are  on  the  opposite 
side.  Strong  xti)iii(/al!oii  oi'  Keiixorrj  wervea  like  the  .•<cm/(V' eause« 
a  rise  in  the  h/ood-jtrrssure.  One  investigator  has,  therefore, 
attempted  to  Mock  the  path  of  the  vasomotor  impulses  l)y  sec- 
tioning the  cord  in  various  ways.  It  Wius  found  tiiat  cutting  the 
lateral  column  on  the  side  opposite  to  that  of  the  nerve  stimulated 
was  followed  by  the  greatest  success.  It  seems  then  that  the  lat- 
eral columns  form  a  very  important  nffermt  jiatlnraif.  Gotch 
and-  Horsely  determined  that  upon  stimulation  of  the  posterior 
roots  80  per  cent,  of  the  impulses  went  to  the  hrain  through  paths 
on  the  same  side  of  the  cord  ;  of  the  remaining  20  per  cent., 
15  per  cent,  went  through  the  dorsal  colunnis  of  the  opposite  side, 
leaving  but  5  per  cent,  for  the  lateral  columns.  Impulses  from 
muscles  and  tendons,  as  well  as  from  the  internal  viscera,  are  be- 
lieved to  pass  cephalad  along  the  direct  cerebellar  tracts  and  by 
the  long-path  til)res  of  the  dorsal  columns.  Dermal  hnpiilxex  may 
pass  through  the  cord  by  short-path  fibres.  Most  of  the  impulses 
from  the  nuclei  of  Goll  an<l  Burdach  pass  to  the  thalamus  and 
then  to  the  central  gyri  of  the  cortex,  but  some  j)ass  to  the  cere- 
bellum by  way  of  the  inferior  pe<luncles. 

Hemisection  of  the  cord  has  marked  effects  on  the  animal  oper- 
ate<l  upon.  For  the  first  few  days  there  is  complete  motor  paral~ 
ysis  of  all  the  parts  sup{)lied  by  nerves  arising  from  the  cord 
below  the  level  of  the  section.  There  are  vasomotor  parahfsis 
and  a  diminution  of  sireat.  The  knee-jerk  h  e.ragr/erated.  Sensa- 
tion is  not  lost,  but  it  appears  dulled.  The  opposite  side  of  the 
body  is  not  affected  by  motor  or  sensory  paralysis.  In  a  few  days 
sensation  returns  on  the  side  operated,  and  in  time  it  becomes 
difficult  to  determine  that  paralysis  exists.  The  limb,  however, 
remains  permanently  thinner.  If  the  hemisection  is  made  above 
the  level  of  the  eighth  cervical  nerve,  the  pupils  are  contracted 
permanently,  but,  nevertheless,  react  to  light  and  shade.  The 
dilator  and  jtilomotor  nerves  of  the  cervical  si^mpathetic  are 
unaltered. 

[i)ij)itlse-'<  reaching  the  cortex  give  rise  to  others  that  ])ass  out 
of  the  central  system  and  cause  a  response  in  various  peripheral 
structures  of  the  body,  just  as  was  the  case  in  pure  reflexes.  To 
determine  the  descending  paths  of  these  impulses,  it  is  customary 


182 


CENTRAL  NERVOUS  SYSTEM. 


to  investigate  the  cerebral  cortex  by  means  of  electrical  or  mechan- 
ical excitation,  or  by  means  of  lesions. 

An  electrical  stimulus,  if  of  proper  strength,  will  usually  bring 
out  well-coordinated  movements,  which  last  longer  than  the  stim- 
ulus. As  the  excitation  becomes  too  great  the  movements  become 
convulsive.  It  has  been  found  by  this  method  of  investigation 
that  the  cerebral  cortex  can  be  divided  into  areas  which  are  con- 
nected with  definite  portions  of  the  body.     These  areas  are  either 


Plan  of  the  human  brain  in  profile  (Dalton),  showing  its  fissures  and  convolu- 
tions :  S,  Fissure  of  Sylvius  ;  S' ,  anterior  branch  ;  S",  posterior  branch ;  R,  fissure 
of  Rolando ;  P,  parietal  fissure. 

sensory  or  motor.     Each  motor  region  upon  stimulation  will  call 
out  movements  of  certain  muscles. 

The  fibres  from  the  motor  cells  of  the  cortex  pass  directly  into 
the  substance  of  the  brain,  which  is  shown  by  making  circular 
incisions  about  various  areas,  when  their  usual  responses  to  exci- 
tation are  not  altered.  A  cut  parallel  to  the  surface  of  the  cortex, 
however,  renders  stimulation  of  the  area  ineffective.  The  paths 
of  the  fibres  from  the  cortex  are  investigated  by  destroying  the 


CENTi:.  I L    .\7v7.'  \ '()  I S  SYSTIJM. 


18:J 


cortical  celln,  when  [he  fibres  with  wliicli  tlicy  wore  in  coimection 
tlogenerate.  Jiy  tliis  inctliod  it  lias  hi't-ii  liniiul  that  the  axoiifx 
of  the  motor  ccll.-<  extend  throiiirli  th(^  IntrDiol  ntj)iinh\  throu^rii 
the  criistd,  and  the  pjintmltlH  to  the  Imlh-rord.  It  is  found  tliat 
some  iil)rcs  of  the  caUoxnm  also  (hrjnu-roti',  and  may  he  traced 
down  through  the  internal  capsule  aud  crusta  of  the  other  side. 

Fi(.i.  41. 


9  -/ 


Brain  of  monkey,  showinyrthe  position  of  the  motor  and  sensory  centres  as  ascer- 
tained l)y  Ferrier.  Tlie  actions  all  occur  on  the  side  of  the  tmdy  opposite  to  the 
part  of  tile  bruin  irritated  :  1,  the  eyes  open  widely,  the  ]iiiiiils  dilate,  and  head  and 
eyes  turn  toward  npimsite  side  :  2,  extension  furwiinl  <«f  the  oTijMisite  arm  and  hand, 
as  if  to  reach  something  in  front:  .>,  movements  of  tail  (ancl  trunk);  4,  retraction 
with  adduction  of  opposite  arm  ;  .^,  supination  and  tlexion  of  the  forearm,  by  which 
the  arm  is  raised  toward  the  mouth  :  I'l,  action  of  zypromatics,  by  whicli  the  anf;le 
of  mouth  is  retracted  and  elevated:  7,  elevatinn  of  ala  of  nose  and  upper  lip:  8, 
openin^r  of  mouth  witli  i>rotrusion  of  tonsrue  :  ;•,  ri'traction  of  tonpue:  lo,  retraction 
of  opposite  angle  of  niuuth  ;  (7,  b.  r,  d,  preliensile  movenu'nts :  11,  retraction  and 
adduction  of  opposite  arm:  I.',  advance  of  the  opposite  hind  liml);  13,  complex 
movements  of  thigh,  leg,  and  foot:  14, 15,  vision  (sensory);  IR,  hearing  (sensory;. 


At  the  decussation  of  the.  pjiraniids  the  irreater  ininiher  of  the 
fii)res  from  the  internal  capsule  of  each  side  cross  to  the  opposite 
side,  and  when  they  reach  the  cord  are  jTrouped  together  to 
form  the  crossf'<1  piiramidal  trart  oi'  the  latrral  cohnnnx.  A  les.<er 
number  of  the  fibres  pa.ss  down  into  the  cord  on  the  same  side 
and  form  the  direct  j>yramidiil  tractx  of  the  a)itcrior  columns. 
Injury  to  the  cortex  of  one  hemisphere  will    produce  degenera- 


184  CENTRAL  NERVOUS  SYSTEM. 

tion  of  the  cross-pyramidal  tracts  of  both  sides,  but  that  on  the  side 
opposite  the  lesion  is  much  more  marked.  The  direct  pyramidal 
tracts  are  well  defined  in  man  and  monkeys,  but  extend  only  to 
the  mid-dorsal  region.  Before  their  termination  they  cross  to  the 
other  side  of  the  cord  in  the  gray  commissure.  The  motor  fibres 
of  both  pyramidal  tracts  end  in  relation  with  motor  cells  in  the 
anterior  horns  of  the  spinal  cord,  which  cells  in  turn  send  their 
axones  to  the  muscles  by  way  of  the  anterior  spinal  nerve-roots. 

There  is  no  direct  relation  between  the  size  of  a  cortical  motor 
area  and  the  mass  of  the  muscles  that  it  controls,  but  the  size  is 
correlated  with  the  complexity  of  the  reactions  that  the  muscles 
take  part  in.  Each  region  is  divisible  into  subsidiary  areas.  For 
instance,  if  the  electrodes  are  moved  from  one  limit  of  the  arm- 
area  to  the  other,  there  will  be  a  regular  contraction  of  the  mus- 
cles from  the  shoulder  to  the  phalanges.  Areas  thus  called  motor 
are  not  purely  so,  for  they  also  contain  fibres  that  bring  afferent 
impulses  from  the  skin,  muscles,  tendons,  or  viscera  to  the  cortex. 
There  are  some  purely  sensory  areas  which  produce  no  response 
on  stimulation.     Of  these,  there  are  four  principal  ones  : 

1.  The  olfactory  area,  which  extends  over  the  uncinate  gyrus, 
the  gyrus  hippocampi,  and  a  part  of  the  gyrus  fornicatus  near  the 
callosum. 

2.  The  visual  area,  which  is  found  about  the  calcarine  fissure, 
all  through  the  cuneus  extending  to  the  occipital  lobe. 

3.  The  auditory  area,  which  includes  the  transverse  gyri  in  the 
Sylvian  fissure  and  the  first  temporal  gyrus. 

4.  The  body-sense  area,  which  is  found  about  the  two  central 
gyri  and  extends  forward  to  the  frontal  gyri,  and  from  the  pre- 
cuneus over  one-half  of  the  mesial  surface  of  the  hemisphere. 

As  the  result  of  common  experience  it  is  known  that  a  motor 
response  may  follow  any  sensory  stimulation  whatsoever,  so  that 
motor  and  sensory  areas  must  be  connected.  The  fibres  that  bring 
this  about  are  called  association-fibres.  Their  function  is  to  fur- 
nish pathways  which  are  more  or  less  intricate  between  different 
areas,  and  to  retain  previous  impressions  as  memories  which 
modify  any  other  impulses  passing  over  them.  When  the  motor 
and  sensory  areas  are  contrasted  with  the  surface  that  remains  of 
the  cortex,  it  is  found  that  extensive  areas  give  no  response  upon 
direct  stimulation.  They  may  be  designated  as  latent  areas. 
They  include  the  ventral  surface  of  the  hemisphere,  a  considerable 


CESTRAL  MinVOVS  SYSTEM.  185 

portion  of"  the  ni(!.sijil  surfju'c,  and  parts  of  tlie  frontal,  parietal, 
and  temporal  lohos.  The  frontal  rej^ion  is  conni'eted  liy  iihrea 
with  the  |)ons  and  eerehelhiiii.  Removal  of  this  portion  of  the 
brain  is  followed  hy  transient  sensory  and  motor  ilislurliaiices. 
Jinnoi'dl  of  hoth  lohes  eanses  the  animal  to  lose  all  curiosity, 
atJeetion,  pleasure,  and  capacity  to  learn.  It  is  in  this  portion  of 
the  brain  that  the  intelligence  is  centred  ;  it  is  the  organ  of  the 
mind.  Memory,  reason,  emotions,  and  all  the  other  attributes  of 
the  mind  are  <lej)endent  upon  its  functional  power.  There  are 
instiinces  in  which  injury  or  disease  of  one  half  of  the  cerebrum 
has  lett  the  intellectual  faculties  not  gravely  impaired.  From  a 
consideration  of  such  cases  it  has  been  held  that  tlie  action  of  one 
of  the  hemispheres  is  sutticient  for  the  ))urposes  of  the  nnnd  ;  but, 
as  a  rule,  it  is  safe  to  say  that  the  liemixpheres  act  in  uniaon.  lu 
some  of  the  lower  animals  the  cerebrum  may  be  removed  entirely 
without  killing  them.  When  this  is  done  in  the  case  of  a  pigeon, 
the  bird  remains  quietly  in  one  position,  and  is  not  disturbed  by 
noises  ;  if  thrown  from  its  perch,  it  flies  and  alights  in  a  nearly 
normal  manner.  If  a  foot  be  pinched,  it  withdraws  it  and  perhaps 
changes  its  position.  The  bird  is  capable  of  reflex  actions  of 
various  comi)licated  kinds,  but  there  is  no  spontaneous  exercise 
of  volition,  and  all  its  movements  are  excited  by  nerve-stimuli 
from  without,  of  the  moment  of  which  it  has  no  perception. 

The  cerebellum  seems  to  exert  no  influence  upon  the  sensory 
nerves,  for  sensibility  is  not  affected  by  its  injury.  The  motor 
Kilxtem  of  the  body  is.  however,  entirely  di.sorganized  by  lesions  of 
this  organ,  giving  rise  to  extreme  hicoonJiniitioit.  The  two  halves 
of  the  cerebellum  are  unitetl  liy  connnissural  fibres,  division  of  which 
is  followed  by  a  transitory  disturbance  in  the  gait.  The  ccrehel- 
Inm  is  not  conceriird  with  pxijchlcal  fitDctiona.  When  small  por- 
tions are  removed,  the  animals  become  feeble  and  uncertain  in 
their  movements,  but  are  able  to  move  about  for  ordinary  pur- 
fjoses.  As  the  amount  removed  is  increased,  the  want  of  co()r«li- 
nation  of  the  voluntary  mu.«icles  becomes  greater.  With  the 
entire  cerebellum  gone,  the  condition  is  absolute — animals  cannot 
stand  or  walk,  or  bring  any  of  the  muscles  into  orderly  action. 
If  the  animal  is  laid  upon  the  back,  it  cannot  recover  itself  but 
strugsrles  in  vain.  The  senses  are  normal  and  the  will  is  present, 
for  if  a  blow  is  threatened  an  attempt  is  matle  to  avoid  it.  When 
the  le.sion  is  confined  to  one  hemis|)here.  the  lack  of  coiirdiuatiou 


186 


CENTRAL  NERVOUS  SYSTEM. 


is  noticed  in  the  opposite  side  of  the  body.  Under  these  circum- 
stances the  animals  fall  to  the  opposite  side  and  roll  over,  giving 
rise  to  what  are  known  as  forced  movements.  Pigeons  from  which 
the  cerebellum  is  removed  may  live  sometimes  for  months,  and  in 
some  cases  after  partial  removal  there  is  a  return  of  the  power  to 
coordinate  at  the  end  of  some  days. 

The  function  of  the  thalamus  is  not  well  understood.     Fibres 
reach  its  ventral  portion  from  the  cord,  and  the  cells  in  relation 

Fig.  42. 


Jl->^^:- 


/  #  /    f  0$i0W 


Diasram  of  human  brain  in  transverse  vertical  section  (Dalton):  1,  tuber  an- 
nulare :  2,  2,  crura  cerebri ;  3,  3,  internal  capsule;  4,  4,  corona  radiata ;  5,  6,  cerebral 
ganglia ;  7,  corpus  callosum. 

with  which  they  end  send  their  axones  to  the  cerebral  cortex. 
Some  cells  in  the  cortex,  in  turn,  send  axones  back  to  the  thala- 
mus. Cell-groups  which  increase  the  responsiveness  of  the  central 
system  are  probably  located  here.  Lesions  are  accompanied  by 
a  loss  of  power  to  express  the  emotions  through  the  muscles  of 
the  face.  When  they  extend  to  the  internal  capsule  and  to  the 
crura  cerebri,  paralysis  results. 

Lesions  in  the  crura  lead  to  paralysis  of  the  opposite  side  of  the 


CENTRAL  NERVOUS  SYSTEM.  1m7 

l)ody,  both  of  sensation  and  of  motion,  of  a  degree  depending  npon 
tiie  extent  of  the  lesions  ;  and,  besides,  result  in  a  paralysis  of 
the  motor  oeuli  nerve  of  the  same  side  aa  the  lesions.  There  is  a 
derangement  of  the  ooilnlination  of  movements,  sliown  in  rotary 
movements  when  the  suhjeet  attempts  to  walk.  It  is  inferred  that 
co'irdinating  im|)ulses  pass  througli  the  crura. 

The  a)ik'rior  cor/ioni  (ji((alri(iriiiiii<i  are  the  homologues  of  the 
optic  lobes  in  some  of  the  lower  animals,  and  the  anterior  pair 
may  be  regarded  as  important  centres  for  the  rixiKtl  and  motor 
fanctionn  of  the  ei/es.  The  posterior  pair  are  associated  more 
intimately  with  the  sense  of  hearing.  Not  only  does  blindness 
follow  lesions  of  the  anterior  pair,  but  often  they  are  atrophied 
when  the  eyes  are  destroyed.  Crossed  paralysis  may  follow  lesions 
in  the  lower  portion  of  the  pons,  which  is  more  or  less  complete, 
together  with  a  paralysis  of  the  facial  muscles  on  the  same  side  as 
the  lesions. 

As  the  mednUa  is  the  sole  connecting  link  between  the  upper 
part  of  the  brain  and  the  cord,  it  necessarily  contains  all  fibres 
passing  between  these  limits,  so  that  it  conducts  all  impulses.  It 
resembles  the  spinal  cord  in  being  the  seat  of  reflex  acts  ;  the  only 
difference  between  them  being  in  the  fact  that  many  of  the  reflexes 
performed  by  the  bulb  are  cf  much  greater  importance  to  life. 
There  is  a  considerable  number  of  centres  in  the  medulla  which 
control  important  and  comidicated  coiirdinated  muscular  actions. 
These  are  centres  for  reflex  action  for  the  most  part,  which  are 
called  upon  to  act  in  response  to  stimuli  derived  from  an  afferent 
impulse  or  to  a  voluntary  effort.  As  examples,  may  be  mentioned  : 
the  cardiac  centre,  the  vasomotor  centre,  the  thermotactic  centre, 
and  the  respirator]!  centre.  The  latter  may  be  easily  demonstrated 
in  the  frog.  If  the  spinal  cord  be  removed  up  to  the  meilulla, 
the  respirations  will  continue,  and  in  the  same  way  they  will  not 
cease  if  the  hemispheres  also  are  removed.  If  the  medulla  is 
then  injured  at  the  origin  of  the  pneumogastric  nerve,  the  move- 
ments of  respiration  cease.  The  same  occurs  when  the  medulla  is 
broken  in  man  near  the  axis  in  executions  by  hanging. 

Divixion  of  the  spinal  cord  results  in  a  complete  loss  of  conduc- 
tivity between  the  two  segments.  There  are  a  loss  of  sensation  and 
a  paralysis  of  the  parts  supjilied  by  nerves  emerging  from  the  cord 
iielow  the  section.  I^oth  spirments  of  the  cord  may  suffice  for  cer- 
tain reflex  movements.      If  the  sn-tion  be  maile  al)ove  the  point  of 


188  CENTRAL  NERVOUS  SYSTEM. 

origin  of  the  phrenic  nerves,  death  from  asjohyxia  results.  In  the 
frog,  whose  spinal  cord  has  been  cut  close  to  the  medulla  and  the 
medulla  destroyed,  the  following  results  are  noticed  :  the  animal 
does  not  respire  through  its  lungs  and  lies  prone  on  its  belly.  If 
dropped  into  a  basin  of  water,  it  sinks,  making  no  attempt  to  swim ; 
it  does  not  swallow  food.  If  the  section  is  made  anterior  to  the 
bulb,  the  frog  breathes,  sits  in  a  normal  position,  swims  in  a  basin 
of  water,  crawls  out  if  it  can  and  then  sits  still.  It  makes  no 
motion  unless  irritated,  then  hops  away.  It  swallows  food  placed 
upon  the  tongue. 

Cranial  Nerves. 

The  cranial  nerves  are  varied  in  their  functions,  and  all  arise 
from  ganglia  of  gray  matter  in  the  brain  and  medulla.  The  floor 
of  the  fourth  ventricle  is  distinguished  particularly  by  the  abun- 
dance of  nuclei  from  which  the  cranial  nerves  arise. 

I.  The  olfactory  nerve  forms  the  pathway  for  the  impulses  giving 
rise  to  smell.  The  fibres  pass  from  the  sense-endings  of  the  nose 
to  the  olfactory  bulb  on  the  same  side,  and  then  by  way  of  the 
olfactory  tract  to  the  gyrus  fornicatus  or  to  the  temporal  end  of  the 
gyrus  hippocampi. 

II.  The  optic  nerve  conducts  impulses  from  the  retina  to  the 
pulvinar,  the  corpora  quadrigemina,  and  the  external  geniculate 
bodies.  In  man  the  fibres  for  the  greater  part  cross  in  the  chiasma. 
From  the  primary  centres  they  are  continued  to  the  occipital  cortex 
of  the  same  side,  passing  through  the  occipital  end  of  the  internal 
capsule.  The  location  of  the  centres  is  probably  in  the  cuneus  and 
surrounding  parts.  The  calcarine  fissure  has  been  indicated  by 
some  as  the  most  important  ending. 

III.  The  motor  oculi  is  a  purely  motor  nerve.  Section  paralyzes 
the  elevator  of  the  upper  eyelid,  giving  rise  to  ptosis ;  paralysis 
of  the  muscles  of  the  eyeball  results  in  inability  to  move  the  eye 
up,  down,  or  inward,  while  the  unopposed  action  of  the  external 
rectus  produces  external  strabismus ;  paralysis  of  the  muscle  of 
the  iris  causes  the  pupil  to  remain  dilated,  so  that  it  does  not  re- 
spond to  light ;  paralysis  of  the  ciliary  muscle  prevents  accommo- 
dation. The  control  of  the  pupil  through  a  strong  voluntary  effort 
exerted  through  the  third  nerve  shows  itself  in  a  contraction,  as 
when  the  eyeball  is  turned  strongly  upward  and  inward. 

IV.  The  patheticus  supplies  the  superior  oblique  muscle.     Its 


CESTRAL   SKRVOUS  SYSTKM. 


189 


section  results  in  douhk'  vision,  and  the  image  seen  hv  the  afrt-ftecl 
eye  ai)pears  oMicjiicly  and  Ik-Iuw  that  of  the  othiT  eye.  This  may 
be  corrected   hy   inclining  the   head  to  the  opposite  side. 

Fig.  43. 


View  of  the  posterior  surface  of  the  imdullii,  the  ronf  of  the  fourth  ventricle 
beinp  removed  to  show  the  rhomboid  sinus  dourly.  The  left  half  of  the  figure 
represents  :  Cn.  funiculus  cuneatus  and,  q,  funiculus  gracilis  :  O,  obex  :  ■••■}}.  nucleus 
of  the  spinal  accessory;  p,  nucleus  of  the  pneuniogastric ;  p  +  8p.  ala  cincra;  R, 
restiform  bf>dy;  XII',  nucleus  of  the  hypoglossal:  ^  funiculus  teres:  a,  nucleus 
of  the  acusticus;  m,  stria-  mcdullares:  i,-,  and  3.  middle,  su]>eri()r,  and  inferior 
cerebellar  peduncle,  respectively  :  /,  fovea  anterior:  J,  eniinentia  teres  igenu  nervi 
facialis) :  n,  locus  cooruleus.  The  right  half  of  the  figure  represents  the  nerve-nuclei 
diagranimatieally :  I',  motor  trigeminal  nucleus:  I',  median,  and  l",  inferior  sen- 
sory trigemiiuil  nuclei :  17,  n\iclc\is  of  abduccMis:  177,  facial  nucleus:  1777,  poste- 
rior median  acoustic  nucleus:  1777'.  anterior  meiiian  ;  17/7",  posterior  lateral; 
VIII'",  anterior  lateral  acoustic  nuclei :  7A',  glossopharyngeal  nucleus:  A',  A7,  and 
A'/7,  nuclei  of  vagus,  spinal  accessory,  and  liypoglossal  nerves,  respectively.  The 
Roman  numerals  at  the  side  of  the  figure,  from  I'to  A7/,  represent  the  correspond- 
ing nerve-roots  (Erb). 


V.  The  tn'rfeyninus  )ierve  breaks  up  into  three  branches :  of 
these,  the  first  and  seconrl  are  entirely  sensory,  while  the  third  is 
motor.     Section  of  the  motor  root  of  the  nerve  results  in  a  paral- 


190 


CENTRAL  NERVOUS  SYSTEM. 


Fig.  44. 


ysis  of  the  muscles  of  mastication.      Destruction  of  the  sensory 
root  results  in  complete  anaesthesia  of  the  skin  of  the  face  and  the 

mucous  membrane  of  the  mouth. 
The  anaesthesia  of  the  conjunc- 
tiva, of  the  nostrils,  and  of  the 
lips  prevents  the  reflex  self-pro- 
tection which  belongs  to  the  parts, 
and  they  become  easily  injured. 
The  nerve-cells  are  located  in  the 
Gasserian  ganglion.  The  periph- 
eral axones  extend  to  the  skin, 
while  the  central  axones  upon 
reaching  the  bulb  divide  into  a 
shorter  branch,  which  extends 
cephalad  and  a  longer  branch 
which  extends  caudad,  both  con- 
necting with  cells  in  the  sub- 
stantia gelatinosa.  One  set  of 
neurones  is  thought  to  pass  di- 
rect to  the  cerebellum. 

VI.  The  abducens  supplies  the 
external  rectus  muscle  of  the  eye. 

VII.  The  facial  is  a  motor 
nerve  which  parallels  in  its  dis- 
tribution the  sensory  portion  of 
the  fifth.  It  supplies  the  super- 
ficial muscles  which  give  the 
power  to  the  features  reflecting 
the  emotions.  If  the  nerve  is 
sectioned,  the  face  on  that  side  is 
devoid  of  motion  and  becomes 
smooth  and  expressionless.  The 
eyelids  do  not  close  and  the  lips 
do  not  oppose  properly  on  account 
of  the  defective  action  of  the  or- 
bicularis muscle.  There  is  difii- 
culty  in  drinking  and  in  speaking 
for  the  same  reason. 

VIII.  The  cochlear  jwrtion  of  the  auditory  is   the   nerve  of 
hearing.     The  cell-bodies  of  these  fibres  are  situated  in  the  spiral 


A  partly  diagrammatic  view  of  the 
floor  of  the  aqueduct,  looking  upward 
(dorsally),  nuclei  of  the  third  and 
fourth  nerves,  and  the  decussating 
fibres  of  the  latter  all  shown;  the 
third  nerve  nuclei  are  subdivided 
into  an  anterior  nucleus,  the  Edinger- 
Westphal  nucleus  fa  and  h),  and  a 
posterior  nucleus ;  the  ijosterior  nu- 
cleus has  a  dorsal,  a  ventral  and  a 
mesial  portion;  the  decussation  of 
the  fibres  from  the  dorsal  portion  of 
the  posterior  nucleus  of  the  third 
nerve  is  shown.    (Edinger.) 


ci:\ TIL  I  /.  m:i:  \ 'o  i  's  s  ystem. 


IIJI 


paii<rlion  of  (he  coclilfji.  which  is  hoiiiuhj^-otis  wilh  the  dor.-al  root- 
,ir:iiitrli:i  of  spinal  iicrvcs.  One  axoiic  reaches  tlic  oriran  of  ('orti, 
jiiitl  the  olhcr  passes  to  the  hull),  where  it  terminates  either  in  (he 
dorsal  or  ventral  nucleus  of  (he  eii,Mi(h  nerve.      The  lihres entering 


Fui.  45. 


niaprain  of  tlio  fifth  nerve  and  its  distribution  :  1,  sensitive  root:  2,  motor  root ; 
3,  (iasserinn  Ranslion  :  I.  ophtluilmic  divisicm  ;  II,  superior  maxillary  division  ;  III, 
inferior  niiixillary  division:  4,  sui)raorbital  nerve,  distributed  to  the  skin  of  the 
forehead,  inner  aiiirle  of  the  eye.  and  r'n)t  of  the  nf)se  ;  'i,  infraorbital  nerve,  to  the 
skin  of  the  lower  eyelid,  side  of  the  nose,  and  skin  and  mucous  membrane  of  the 
niilierliji:  ti,  mental  nerve,  to  the  integument  of  the  ehin  and  edtre  of  the  lower 
jaw,  antl  skin  and  mueo\i.s  membrane  <if  the  lower  lip;  n,  u,  external  terminations 
of  the  nasal  braiieh  of  tlie  ophthalmic  division,  to  the  mucous  membrane  of  the 
inner  part  of  the  eye  and  the  nasal  passasres,  and  to  the  base,  tip,  and  win?  of  the 
nose:  ^  temporal  branch  of  the  superior  nnixillary  division,  to  the  skin  fif  the  tem- 
poral rei-'ioii :  »»,  malar  branch  of  the  superior  maxillary  division,  to  the  skin  of  the 
cheek  and  neiehborintr  parts:  ^,  Imccal  branch  of  the  inferior  maxillary  division, 
passing  along  tlie  surface  of  the  buccinator  muscle,  and  distributed  to  tlie  mucous 
membrane  of  the  cheek  and  to  the  nnicous  membrane  and  skin  of  the  lips:  /,  linguftl 
nerve,  to  the  mucous  membrane  of  the  anterior  two-thirds  of  the  tomrne  :  nl.  auric- 
ulotemporal branch  of  the  inferior  maxillary  division,  to  the  skin  (.f  the  anterior 
j)art  of  the  external  ear  and  adjacent  temjioral  region  ;  j.r.  x,  muscular  branches, 
to  the  temiioral,  masseter,  and  internal  and  external  pterygoid  muscles:  i/,  muscular 
branch,  to  the  mylohyoid  and  anterior  belly  of  the  digastric ;/,  sensitive  branch 
of  communication  to  the  facial  nerve. 


the  ventral  nucleus  may  be  continued  to  the  superior  quatlrioremina. 
passinir  hv  way  of  the  trapezium.  th(>  superior  olive,  the  lateral 
lemniscus,  and  the  inferior  collicus.  They  may  jrive  collaterals  (o 
each,  or  may  end  iu  any  of  these  gray  masses.     Cells  of  the  dorsal 


192 


CENTRAL  NERVOUS  SYSTEM. 


nucleus  send  their  axones  across  the  floor  of  the  fourth  ventricle, 
forming  the  strise  acusticse. 

The  vestibular  portion  of  the  eighth  nerve  transmits  impulses 
from  the  ampullae  of  the  semicircular  canals,  and  therefore  serves 
the  sense  of  equilibrium.  The  cell-bodies  of  these  fibres  are 
located  in  the  vestibular  ganglion,  and  their  central  axones  are 

Fig.  46. 


Diagram  of  the  facial  nerve  and  its  distribution :  1,  facial  nerve  at  its  entrance 
into  the  internal  auditory  meatus;  2,  its  exit  at  the  stylomastoid  foramen;  3,  4, 
temporal  and  posterior  auricular  branches,  distributed  to  the  muscks  of  the  exter- 
nal ear  and  to  the  occipitalis ;  5,  branches  to  the  frontalis  muscle  ;  6,  branches  to  the 
stylohyoid  and  digastric  muscles;  7,  branches  to  the  upper  part  of  the  platysma 
myoides ;  8,  branch  of  communication  with  the  superficial  cervical  nerve  of  the 
cervical  plexus. 


divided  into  a  branch  passing  cephalad  and  one  passing  caudad, 
which  terminate  with  various  nuclei,  and  also  pass  to  the 
cerebellum. 

IX.  The  glossopharyngeal  nerve  is  the  nerve  of  taste  and  of 
deglutition.  It  is  motor  as  well  as  sensory  in  function.  Its  dis- 
tribution is  to  all  the  muscles  of  deglutition,  and  stimulation 
contracts,  while   section    paralyzes   them.      The  very    numerous 


WKiaiiT  AM>  ciiowrn  III-  nil',  iuims.         \\y.\ 

comu'clioiis  of  tlu-  iiorvi'  comiylifalr  ils  ()ii;.'-iii  and  iiitcrirrc  with 
a  clear  coiiiiJrc^luMision  of  llu'  unaided  I'unclioii  n|'  liu-  nerve.  The 
cells  of  the  tihress  lie  in  the  huilt  on  the  medial  siile  oi"  the  tractiid 
solitarius.  Their  axoiie.s  are  sent  ci'|ihalad  lhriiu,i,di  the  medial 
lemniscus.  Lalcd  bivcdUjdlion--*  have  kIioivh  that  the  chief  path  af 
the  t<idr-.-<rii.-<e  Ix  over  the  chorda  tympaiil  nerve,  which  leaven  the 
ijhtxKophanjiKjeal  mainhj  a  nerve  of  motor  function. 

X.  The  afferent  Jihres  of  the  vagii.'<  convey  impulses  from  the 
|)lKii-ynx,  (i}st)|)liaunts,  stomach,  liver,  pancrea.s.  sjjleen,  larynx, 
bronchi,  and-  lunirs.  Their  termination  is  near  the  naiul  vital. 
The  functions  of  the  pneumoL'^astrics  are  very  numerous  indeed. 
It  is  involved  in  respiration,  deirlutition,  in  the  movements  of  the 
stomach,  in  the  action  of  the   heart,  linigs,  ami  viscera. 

XI.  The  s}ii)ial  accr.'Oionj  is  a  motor  nerve  essentially,  hut  it 
contains  some  sen.sory  fibres.  iSectiou  produces  paralysis  of  the 
voice,  but  does  not  affect  the  glottis.  Forced  respiration  is 
impaired. 

XII.  The  hypogloxml  is  a  motor  nerve,  but  possesses  some 
sensory  iibres  which  it  derives  from  the  cervical  spinal  nerves 
and  from  the  fifth.  This  nerve  is  important  in  mastication.  In 
animals  its  section  is  followed  by  inability  to  drink  on  accoinit 
of  ilifficulty  in  lapping.  In  man  section  of  the  nerve  prevents 
articulation. 

WEIGHT  AND  GROWTH  OF  THE  BRAIN. 

Weight. — Roughly  it  is  three  pounds  or  about  one-fortieth  of  the 
total  body-weight,  and  this  ratio  is  greater  than  in  the  lower  ani- 
mals, with  a  few  exceptions  among  the  smaller  birds  and  monkeys. 

Weight  of  Brain  in  Gramme><  (To|)inard\ 

Classes.  >rales.  Females. 

Macroc'cplialic 192.")  to  ITOf  174.S  to  1.^01 

Larcro 1700  "  14-j1  1.-)()0  "    1.",")] 

Medium 14-30  "  ]'2.')1  1.S.50  "  ll.")l 

Smalt 12.'>0  "   1001  ILiO  "     Wl 

Microceplialic 1000   "     oOO  900"     28.3 

In    comparinLT    brain-weights,    the    method    of  rt'inoval    of  tlie 
ence|)halon   should  always  be  considered,   since   retention  of    |>ia 
antl  the  fluids  of  the  ventricles  affects  the  result, 
l.-?— Phys. 


194  CENTRAL  NERVOUS  SYSTEM. 

In  Boyd's  method,  after  the  skullcap  has  beeu  removed  but  the 
pia  left  intact,  the  hemispheres  are  sliced  away  in  horizontal  sec- 
tions as  far  down  as  the  tentorium.  By  means  of  a  section  pass- 
ing in  front  of  the  corpora  quadrigemina  the  remainder  of  the 
hemispheres  is  removed.  The  cerebellum,  including  the  quad- 
rigemina, pons,  and  bulb,  is  finally  removed.  Each  portion  is 
weighed  separately.  Sometimes  the  pia  and  the  fluid  within  the 
ventricles  are  included  in  the  weight  of  the  brain,  and  sometimes 
act.  Broca  gives  the  following  table  for  the  weight  of  the  pia, 
for  normal  males : 

20  to  30  years 45  grammes. 

31  "  41      "        50 

60      "        : 60        «' 

The  ventricles  have  a  capacity  of  26  c.c.  of  water. 

In  considering  the  weights  of  different  brains,  it  is  assumed  that 
the  proportion  of  nervous  to  non-nervous  tissue  is  constant,  so  that 
different  weighings  may  be  compared.  If  this  be  the  case,  then 
the  variations  in  weight  may  be  due  to  greater  size  of  the  individ- 
ual nerve-elements,  indicating  a  greater  potential  energy,  or  they 
may  be  due  to  a  greater  number  of  nerve-elements  giving  rise  to 
more  possible  pathways.  A  minute  study  of  the  proportional 
weights  of  different  parts  of  the  brain  shows  that  variations  due 
to  sex,  age,  and  stature  are  very  .constant,  which  is  in  harmony 
with  the  view  that  weight-differences  are  due  to  the  size  of  the 
nerve-elements  rather  than  to  variations  in  their  number.  In  the 
latter  case  brain-weights  would  show  independent  variations  in 
different  parts  of  the  encephalon. 

All  parts  of  the  central  nervous  system  of  males  are  heavier 
than  corresponding  parts  of  females.  The  weight  varies,  in  each, 
directly  with  the  stature  and  inversely  with  old  age.  The  brains 
of  criminals  do  not  differ  in  any  marked  way  from  those  of  ordi- 
nary hospital  patients.  Insane  (excluding  microcephalics)  have 
no  characteristic  brain-weight,  except  in  such  cases  where  a  con- 
gestion of  the  brain  has  occurred,  when  the  weight  is  markedly 
increased  ;  on  the  other  hand,  insanity  due  to  destructive  changes 
of  brain-tissue  is  marked  by  a  low  brain-weight.  As  a  whole, 
individuals  whose  brains  during  the  years  of  growth  have  been 
under  favorable  circumstances  possess  the  heavier  brains.  In 
some  degree  the  size  of  the  brain   bears  a  direct  relation  to  the 


)VF.i<:irr  AM)  <:nn\\rii  or  riii:  hums.  Hi-'i 

hitrlh'ct  of  tlic  iiiilividiial.  Itiit  lliis  is  iiol  ahsulute.  Tlic  (Icplli  of 
the  sulci  ami  llu-  coiistMniciit  size  aii<l  coiiiiilcxity  of  lli<-  convolu- 
tions are  a  more  clHcieut  measure  of  the  hrain  j)o\\er.  In  the 
hirjrest  of  the  apes  the  Itraiii  of  an  adult  animal  is  ahout  the  same 
in  weijjrht  as  that  of  a  human  infant  at    hirth. 

Wihjht  of  Cord. — The  aveniirc  wciLdit  of  the  spinal  cord  is 
ahout  2l).27  grammes,  without  the  m-rvc- roots,  hut  the  pia  intact. 
It  is  prol)al)le  that  this  weijrhl  varies,  like  tiial  of  the  hrain,  with 
ajje,  sex,  and  stature. 

Growth  of  Brain. — At  hirlh  the  hrain-weiirhl  is  ahout  one-third 
of  what  it  will  he  at  maturity.  The  increase  is  very  rapid  during 
the  tirst  year  ;  quite  rapid  (luring  the  next  seven  or  eight  years; 
after  this  it  hecomes  very  slow.  The  maximum  weight  is  attained 
in  men  hetween  the  fiftieth  and  sixtieth  years ;  in  women,  between 
the  fortieth  and  fiftieth  yeai-s.  A  '' prnnu.rimnm'"  at  thirteen  to 
fifteen  for  males  and  at  ahout  fourteen  for  females,  indicating 
a  too  vigorous  growth,  seems  to  be  an  important  cause  of  death  at 
this  age.  The  eneeplialon  reaches  maturity  much  sooner  than 
the  body  as  a  whole.  At  the  end  of  the  eighth  year,  when  the 
brain  has  almost  completed  its  growth,  the  body  has  reached  but 
a  third  of  its  mature  weight.  At  birth  the  brain  forms  12  per 
cent,  of  the  total  weight  of  the  body,  while  in  the  adult  it  forms 
but  2  per  cent.,  or  even  less. 

It  has  ])een  estimated  that  the  cortex  alone  contains  ^200  mil- 
lion cell-bodies,  and  that  the  entire  nervous  system  must  contain 
at  least  lo,()()()  million  cells.  It  is  generally  iKjreed  that  in  the 
htnudii  he'uKj  tlic  number  is  not  increased  after  the  third  month  of 
fatal  life.  All  subsequent  increase  in  the  mass  of  the  brain  is 
therefore  due  to  an  enlargement  of  individual  cells.  There  is 
very  little  direct  evidence  for  this  in  man.  Kaiser  has  measured 
the  diameters  of  the  cells  of  the  anterior  horns  of  the  spinal  cord, 
and  in  this  manner  has  determined  an  increase  in  size.  In  the 
frog  there  is  a  gradual  increase  in  the  nund)er  of  fibres  of  the 
ventral  and  dorsal  spinal  nerve-roots.  The  rate  of  increase  is 
about  50  fibres  for  the  ventral  roots  and  70  fibres  for  the  dorsal 
roots  for  each  gramme  increase  in  the  weight  of  the  frog.  More- 
over, the  greatest  number  of  medullate<l  fibres  is  to  be  foinid  in 
the  ventral  roots  near  the  cord,  and  in  the  iU)rsal  roots  near  the 
ganglion.  This  is  explained  by  assuming  undeveloped  cells  which 
grailuallv  become  mature,  and  in  so  doing  push  out  thi-ir  processes. 


196  CENTRAL  NERVOUS  SYSTEM. 

The  area  of  the  cerebral  cortex  which  is  exposed  has  about  one- 
half  the  extent  of  that  which  forms  the  walls  of  the  sulci.  It  has 
been  shown  that  the  fibres  of  the  cortex  are  greater  in  number  in 
middle  age  than  in  youth  or  old  age.  The  association-fibres, 
moreover,  form  three  parallel  systems.  The  deepest  of  these  is 
first  to  become  medullated,  and  the  middle  layer  last. 

The  average  specific  gravity  of  the  brain  for  males  is  about 
1036.3,  and  for  females  1036.  The  gray  matter  has  about  81 
per  cent,  of  water,  and  the  white  matter  about  70  per  cent.  The 
amount  diminishes  from  birth  to  maturity.  Between  the  fiftieth  and 
sixtieth  years  the  brain  loses  in  weight  in  all  parts,  but  the  loss  in  the 
cerebral  hemispheres  is  slightly  greater  than  in  other  portions.  The 
entire  cerebral  cortex  diminishes  in  thickness  with  age,  but  more  in 
motor  than  in  sensory  areas.  In  the  cerebellum  the  branches  of 
the  arbor  vitee  decrease  in  number  and  size  ;  some  of  the  cells  are 
found  to  be  shrunken,  while  the  cells  of  Purkinje  disappear  alto- 
gether. In  the  cord,  especially  in  the  lumbar  region,  the  cells 
become  shrunken,  pigmented,  and  degenerate ;  the  supporting 
tissue  is  increased,  and  the  walls  of  the  bloodvessels  are  thickened. 
In  paralysis  agitans  similar  but  more  marked  changes  occur. 
With  the  advance  of  age  the  entire  central  nervous  system  breaks 
down  into  groups  of  elements,  so  that  its  powers  are  lost  in  an 
irregular  and  disjointed  manner. 

Fatigue. — When  by  voluntary  contractions  of  the  muscles  of 
the  index  finger  a  moderately  heavy  weight  is  raised  at  regular 
intervals,  it  is  found  that  the  height  of  the  contractions  gradually 
decreases,  so  that  in  time  the  weight  can  no  longer  be  lifted.  If 
the  efifort  is  continued,  it  is  found,  in  some  people  at  least,  that  the 
power  of  contraction  returns  periodically  to  nearly  its  normal 
strength,  so  that  a  record  of  the  contractions  presents  a  series  of 
waves.  The  local  feeling  of  fatigue  in  this  case  is  probably  due, 
to  a  great  extent,  to  the  organs  of  muscular  sense.  An  explana- 
tion of  the  general  fatigue  which  may  result  is  to  be  found  in 
Mosso's  experiment,  in  which  he  injected  the  blood  of  a  fatigued 
animal  into  the  circulation  of  a  normal  one,  giving  rise  in  the 
latter  to  all  the  symptoms  of  fatigue.  It  cannot  be  doubted  that 
muscular  activity  gives  rise  to  products,  most  of  them  as  yet  un- 
known, which  are  carried  to  the  brain  in  the  circulation.  Lactic 
acid  and  the  monophosphates  of  alkali  metals  circulated  through 
a  muscle    produce  in    it  all    the    characters  of   typical    fatigue. 


wi'.icirr  AM)  ciinwrii  or  riii-:  hums.         id; 

Lactic  acid,  althoii^li  loniud  in  miiscli',  !.■?.  however,  not  alone 
respoiisil)le. 

Blood-supply  of  Brain. — In  iri-nenil,  the  <:i|iilhiiv  m-twork  is 
closest  in  the  ^Tay  matter  or  wherever  any  aLrirreLration  of  cell- 
bodies  is  to  1)0  tonnil.  Ilnher  has  <leinoiislratC(l  nerve-lil)re.>^  in 
the  walls  of  the  ve.ssels  of  the  |)ia,  an<l  Kiilliker  claims  to  have 
traced  them  to  vessels  of  the  nervous  substance  proper.  JJut, 
nevertheless,  vaminoior  pJititomeiia  of  the  hrain  are  not  very 
markeil,  so  that  the  cjuautity  of  blood  Howing  through  the  brain 
varies  but  slightly. 

\  general  rise  of  arterial  pressure  causes  the  blood  to  How 
more  rapidly  in  the  cerebral  vessels,  raises  the  venous  pressure 
and  also  the  intracra}iial  j/rcssurc.  To  some  extent  the  latter  is 
compensated  for  by  a  tlow  of  cerebrospinal  Huid  through  the  fora- 
men magnum  into  the  vertebral  canal.  If  the  pressure  continues 
to  rise,  the  distention  of  the  brain  shuts  off  that  outlet.  Increase 
of  jiressure  from  now  on  impedes  the  circulation  through  the 
brain.  It  follows,  therefore,  that  in  pathologi<^al  cases  where 
trephining  of  the  skull  results  beneficially  the  exjdanatiou  may  lie 
in  a  better  blood-flow. 

The  )iif'faholi.-<)))  of  the  central  nervous  .^system  is  not  very  intense. 
This  is  readily  understood  when  it  is  known  that  the  cell-bodies 
equal  only  2  per  cent,  of  the  entire  mass  of  the  brain.  The  rela- 
tive metabolism  is  less  than  that  of  muscles.  During  mental 
activity  blood  pa.^ses  from  the  lind)S  to  the  head,  as  shown  in  ca.«es 
where  a  defect  of  the  cranial  wall  exists.  During  fatigue  the  brain 
becomes  anaemic,  coineiding  with  a  decrease  in  the  force  of  the 
heart-beat  and  of  the  tone  of  the  abdominal  ve.s.seLs. 

Sleep. — This  phenomenon  is  one  of  many  instances  of  the 
rln/thmir  ftHinfle.-<  of  the  central  nervous  systeiu.  F'rom  time  to 
time  all  animals  with  a  well-developed  nervous  system  go  to  sleep, 
during  which  psychieal  activity  is  at  its  lowest  point.  To  reach 
this  condition,  the  most  important  fantrinf/  fitcinr  is  an  exclusion 
of  all  or  most  of  the  impulses  from  the  central  nervous  system. 
In  a  well-known  case  of  8trumpell,  in  which,  from  a  complicated 
antrsthesia,  all  sensory  impul.^es  were  limited  in  their  entrance  to  a 
single  eye  and  a  single  ear,  tlu'  patient  could  be  i>ut  to  sleep  at  will 
by  closing  the  eye  and  stopping  the  ear.  In  aildition,  sleep  has 
been  attril)Uteil  to  the  following  inlluences  : 

1.   ( "hemical  intlueiices  ; 


198  CENTRAL  NERVOUS  SYSTEM. 

2.  Circulatory  influences ; 

3.  Histological  influences. 

Those  who  hold  to  chemical  influences  in  the  production  of 
sleep,  maintain  that  during  normal  activity  of  the  body  various 
substances  are  formed  which  are  circulated  in  the  blood  and  directly 
lessen  the  activity  of  the  nerve-cells  or  indirectly  diminish  the 
supply  of  blood  to  the  brain.  In  the  theories  of  circulatorg  influ- 
ences a  fatigue  of  the  vasomotor  centre  is  looked  upon  as  the  cause 
of  the  anaemia  of  the  brain  resulting  in  sleep.  In  the  third  set  of 
theories  sleep  is  supposed  to  be  due  to  a  separation  of  the  dendrites 
of  the  brain-cells  due  to  a  shrinkage  of  the  nerve-cell  bodies  or  to 
an  intrusion  of  neuroglia-cells  between  them. 

During  sleep  the  capability  of  the  nervous  system  to  transmit 
impulses  is  not  entirely  lost.  The  cerebral  cortex  is  most  affected, 
the  spinal  cord  least.  The  close  relation  between  dreams  and 
external  stimuli  is  well  known,  and  it  has  been  proved  experi- 
mentally that  vasomotor  changes,  induced  by  external  stimuli,  may 
take  place  without  awakening  the  sleeper. 

The  period  of  deep  sleep  is  short  and  falls  within  the  first  two 
hours  after  its  onset.  During  this  time  the  pulse  and  breathing 
are  slower,  the  intestines  and  bladder  are  at  rest,  the  output  of 
carbon  dioxide  is  lessened,  and  the  consumption  of  oxygen  still 
more  so  ;  metabolism  is  less  vigorous  and  the  temperature  falls. 
The  respiration  is  said  to  become  thoracic  in  type  and  to  take  on  a 
more  or  less  pronounced  Cheyne-Stokes  rhythm.  The  visual  axes 
are  probably  parallel  and  directed  to  a  distance,  but  the  pupils  are 
contracted.  The  latter  is  peculiar,  since  an  absence  of  light  should 
bring  about  dilatation.  This  is  connected  perhaps  with  important 
actions  taking  place  in  lower  levels  of  the  brain. 

Loss  of  sleep  is  more  injurious  than  starvation.  Dogs  have  re- 
covered from  a  period  of  starvation  of  twenty  days,  but  a  loss  of 
sleep  of  five  days  proved  fatal.  The  body -temperature  fell  8°  C. 
below  normal  and  the  reflexes  disappeared.  The  red  blood-cor- 
puscles first  were  diminished,  but  later  increased  in  number.  Post- 
mortem examination  revealed  widespread  fatty  degeneration  and 
cerebral  hemorrhage. 

In  experiments  made  by  Patrick  and  Gilbert,  three  subjects 
were  observed  for  ninety  hours  while  being  deprived  of  sleep. 
The  gain  in  weight  which  resulted  was  lost  during  the  first  sleep 
after  the  experiment.     A  decreased  pulse-rate  and  a  lowered  body- 


WEiaiir  AM)  ciiowrii  OF  Till-:  hums.         n»:> 

U'iii|)oratiire  were  observed.  In  jreiieral,  lliere  was  a  loss  of  all 
powers  ex<»']»t   ill  a<'Ut('iiess  of  vision,  wliidi  was  increased. 

Hibernation. — This  is  comiefted  cio.sely  witli  sleep,  occurring 
perioilically  in  many  irroui)S  of  animals  and  in  a  few  manimal.s. 
It  is  characlerized  l»y  a  les-seiieil  metaltolism  resnlliiiLr  from  a  fall 
of  the  e.xternal  temperaliire,  and  may  he  producctl  artificially  in 
summer  hy  cold.  The  hearl  heats  very  slowly  and  not  very  vi;:- 
orously.  while  respiration  is  very  slow  and  feei)le.  ^Nevertheless, 
the  hlood,  arterial  as  well  as  venous,  is  bright  scarlet  in  color, 
owiiiiT  to  the  little  oxyyen  consumed  hy  the  tissues.  A  hihernating 
dormouse  has  been  observed  to  gain  in  weight,  which  was  due  en- 
tirely to  an  exee.ss  of  oxygen  takeu  in.  Muscles  and  nerves 
reinaine<l  irritable,  and  stimulation  of  the  vagus  produces  a  still 
further  slowing  of  the  heart-l)eat. 

Hypnotism. — This  state  is  analogous  to,  but  by  no  means  iden- 
tical wiih,  sleep.  It  ditfers  in  a  peculiar  loss  of  control  over  the 
mu.scular  powers;  in  fre(iueiit  aiuesthesia  and  hypenesthesia  ;  in 
the  great  clearness  of  psychical  images,  which  may  be  forgotten, 
but  are  remembered  in  subseipient  trances.  In  the  lighter  stages 
the  mind  sees  clearly  what  is  going  on  about  it,  which  is  not  true 
in  sleep.  Finally,  hypnosis  is  characterized  by  an  extraordinary 
obedience  to  suggestions.  The  jiower  of  inhibition  residing  in  the 
cerebrum,  by  which  the  mind  is  constantly  controlling  antl  arresting 
reflex  movements,  seems  to  l)e  diminished  if  not  absent.  Verworn 
has  shown  that  the  so-called  hypnotism  in  animals  is  not  due  to  an 
inhibition  from  the  cortex,  since  the  phenomena  are  obtained 
easily  in  decerebrate  individuals. 

Knee-jerk. — If  the  leg  is  placed  in  an  easy  position,  as  when  it 
rests  oil  the  other  leg,  and  a  sharp  blow  is  directed  against  the 
patellar  temlon,  the  foot  will  be  brought  forward  with  a  su<ldeii 
jerk.  This  is  known  as  the  knee-jerk,  and  is  caused  by  the  sudilen 
contraction  of  the  (pmdriceps  femoris.  Physiologists  are  divided 
in  the  explanation  of  this  phenomenon  :  some  regarding  it  as  a 
true  refiex,  while  others  maintain  that  the  contraction  of  the  mu.s- 
cle  is  due  to  a  direct  utimulatiou  of  the  muscle  l)y  vibrations  set 
up  in  the  tense  tendon. 

Con.sidered  as  a  reflex,  the  afl'erent  path  of  the  impul.<es  is 
over  fibres  starting  in  the  patellar  tendon,  running  in  the  anterior 
(•rural  nerve,  and  reaching  the  cord  by  the  jiosterior  root  of  the 
joiirth    lumbar  nerve  in   man.      Tin-  centre  for  the  kiicc-jerk  lies 


200  CENTRAL  NERVOUS  SYSTEM. 

in  the  third  and  fourth  lumbar  segments  of  the  cord.  The  efferent 
path  is  over  fibres  in  the  anterior  crural  nerve  which  leave  the 
cord  by  way  of  the  anterior  roots  of  the  third  and  fourth  lumbar 
nerves.  If  any  portion  of  this  reflex  arc  is  destroyed,  the  knee- 
jerk  is  no  longer  to  be  obtained.  It  may  be  augmented  or 
depressed  by  nervous  impulses  from  many  parts  of  the  central 
nervous  system.  It  is  reenforced  by  cutting  the  nerves  of  the 
antagonistic  muscles,  and  depressed  by  stimulating  the  central 
ends  of  these  nerves.  This  is  explained  by  the  fact  that  flexor 
muscles  send  impulses  to  the  spinal  centre,  and  according  to  their 
condition  influence  the  contractions  of  the  extensors. 

It  is  found  that  a  deficiency  of  the  knee-jerk  exists  usually,  but 
not  always,  with  -a  subnormal  tension  of  the  tendon,  while  a 
hypertonic  state  gives  rise  to  an  exaggerated  jerk.  Thus  section 
of  any  portion  of  the  reflex  arc,  by  lessening  the  tonus  of  the 
muscle,  extinguishes  the  reflex.  It  has  been  claimed  that  the 
time  involved,  0.03  of  a  second,  is  characteristic  of  a  simple  mus- 
cular twitch,  but  too  short  for  a  reflex,  the  briefest  of  which 
requires  more  than  one-fourth  again  as  much  time. 

The  variations  found  in  the  tendon-reflexes  are  very  consider- 
able. In  some  perfectly  healthy  individuals  no  knee-jerk  at  all 
can  be  obtained.  Local  fatigue  of  the  extensor  muscles  dimin- 
ishes it,  while  general  fatigue  at  first  increases  but  later  dimin- 
ishes it  too.  Shutting  off"  the  blood-supply  will  cause  the  knee- 
jerk  to  disappear  in  a  quarter  of  an  hour.  Sthmdi  applied  to  the 
skin,  a  cold  bath  or  friction,  increase  it  if  applied  not  more  than 
0.2  to  0.4  second  before  the  tendon  is  struck.  If  applied  sooner, 
they  cause  an  inhibition  which  reaches  its  maximum  about  1 
second  after  the  stimulus  is  applied,  Sound  always  reenforces 
the  jerk,  while  light  causes  very  little  if  any  inhibition.  Inhala- 
tion of  anaesthetics  (chloroform,  ether)  extinguishes  the  reflex. 
It  has  been  found  in  man  that  the  knee-jerk  was  present  imme- 
diately after  decapitation,  but  usually  injury. to  the  cord  perma- 
nently abolishes  it.  Lombard  has  shown  that  all  the  ordinary 
events  of  daily  life  are  portrayed  faithfully  in  changes  in  the 
knee-jerk.  In  deep  sleep  the  knee-jerk  is  absent,  but  sensory 
stimuli  too  feeble  to  awaken  the  sleeper  are  manifested  in  an 
exaggeration  of  the  tendon-reflexes.  An  increased  knee-jerk  is  a 
symptom  of  some  spinal  diseases.  After  removal  of  the  right 
half  of  the  cerebellum  the  knee-jerk  on  the  homonymous  side  is 


WKICIIT  AM>    aliowm   OF   Till:  HUMS.  'JOl 

more  viixonms.      A  siiiiilnr  ri'Siill  lullous  scdioii  of  IIk-  ci-rclicllMr 
]n'ilmicli's. 

Time  Involved  in  Nervous  Processes. — WIkmicvit  a  in-rvc- 
iiiipiilsc  passes  from  one  neurone  to  another,  there  is  a  delay  in 
its  transmission.  In  the  fro;.',  tor  exanipU',  it  takes  twice  as  hmj: 
tor  an  impulse  to  pass  from  themidtlle  of  the  cereljral  hemisphere.*; 
to  the  optic  lohes  as  from  the  hulh  to  the  lumbar  enlargement, 
allhou<j!:h  the  (li.<tance  i.s  niueli  less.  If  one  eyelid  he  stimulated 
eleetrieally,  hoth  lids  wink.  The  total  time  required  for  this 
reflex  is  from  0.06(5  to  0.057  second.  Deducting  the  time  required 
for  the  impidse  to  pass  to  and  from  the  jirain  along  the  fifth  and 
seventh  nerves,  and  also  the  latent  {)eriod  of  tiie  orbicularis  mus- 
cle, there  remains  O.Of)  to  0.04  second  for  the  time  required  in  the 
bulb.  This  time-value  may  be  regardt'd  as  an  araxKje  of  ximji/e 
rejiex  actions.  The  individual  values  vary  greatly.  In  general 
the  time  is  shorter  the  stronger  the  stimulus.  It  is  shorter  when 
the  reflex  is  confined  to  one  side  of  the  body  than  in  cases  where 
the  impulse  crosses  to  the  other  side,  even  if  allowance  is  made  for 
the  difl'erence  in  the  length  of  the  nervous  ])ath.  The  time 
depends,  of  counse,  on  the  condition  of  the  cord,  becoming  greater 
during  exhaustion  and  di.sease.  The  time  becomes  longer  the 
greater  the  nund)er  of  neurones  involved.  When  the  afi'erent 
impulse  arouses  sensation  and  consciousness,  and  the  ensuing 
response  is  the  result  of  a  volitional  effort,  then  the  neurones 
involved  are  indefinite  in  number.  The  action  is  now  a  reaction, 
and  the  time  is  known  as  the  reaction-time.  This  time  is  shorter 
wheu  the  right  hand  makes  a  response  to  a  stimulus  to  the  left 
than  when  the  response  is  to  either  auditory  or  visual  sensations. 
But  the  shortest  reaction-time  follows  a  visual  excitation  produced 
by  direct  electrical  stimulation  of  the  retina.  Roughly,  reaction- 
times  for  cutaneous,  sensations  are  one-seventh  of  a  second;  for 
auditory  sensations,  one-sixth  of  a  second  ;  for  visual  sensations, 
one-fifth  of  a  second. 

A  reaction-period  consists  of  three  stage.%  corresponding  to  the 
times  re(piireil  by  the  impulse  on  its  afferent  jiath,  its  efferent 
path,  and  in  the  central  nervous  system.  All  three  stages  may 
vary  independently.  The  time  involved  in  the  central  stage  is 
known  as  the  rvdnced  reaction-time.  It  varies  in  different  persons, 
and  is  known  as  the  jjerxoiml  ctjimlion.  When  the  subject  is  re- 
([uired  to  react   to  one  of  two  or  more  p<)ssi!>le  signals,  the   reac- 


202  CE^TBAL  NERVOUS  SYSTEM. 

tion-time  may  be  prolonged  from  0.016  to  0.062  second,  the  time 
varying  with  the  sensation  employed.  It  is  shortened  by  prac- 
tice, so  that  in  time  it  becomes  more  of  the  retiex  type. 

Nerve-centres. — It  is  very  difficult  to  give  a  satisfactory  defini- 
tion of  what  is  meant  by  a  centre.  In  general,  any  portion  of  the 
central  nervous  system  where  impulses  originate  or  undergo  modi- 
fication is  a  centre.  The  modification  of  the  impulse  may  be  in 
strength,  in  direction,  or  in  time.  There  is  no  doubt  that  many 
of  the  so-called  centres  of  the  central  nervous  system  are  not  really 
such,  and  of  the  remainder  all  are  not  equivalent  in  power,  which 
depends  mainly  upon  the  number  of  paths  by  which  impulses 
may  reach  them. 

By  association-centres  are  meant  portions  of  the  cerebral  cortex 
that  lie  between  sensory  centres  and  whose  function  it  is  to  retain 
previous  impressions  as  memories.  Flechsig  calls  the  association- 
centres  "organs  of  thought."  The  conception  of  association-fibres 
and  -centres  gives  an  explanation  of  many  pathological  phenomena. 

In  order  to  do  this,  it  is  necessary  to  assume  association-paths 
between  most  or  all  motor  and  sensory  areas.  These  are  better 
organized  in  some  cases  than  in  others,  so  that  the  communication, 
for  example,  between  visual,  auditory,  and  motor  centres  is  more 
complicated  and  complete  than  that  between  auditory,  gustatory, 
and  motor  centres.  There  exist,  besides,  differences  in  the  two 
hemispheres.  Broca  first  showed  that  a  lesion  of  the  third  frontal 
convolution  of  the  left  hemisphere  resulted  in  a  loss  of  the  power 
of  speech.  It  was  soon  found  that  lesions  of  the  corresponding 
area  of  the  right  hemisphere  do  not  produce  so  great  a  disturb- 
ance, particularly  in  right-handed  persons.  It  is  concluded, 
therefore,  that  in  most  persons  the  speech-centre  is  developed 
more  highly  on  the  left  side.  A  greater  perfection  of  the  right 
eye  and  ear,  involving  corresponding  changes  in  motor  areas,  sus- 
tains the  idea  that  in  these  respects  at  least  the  hemispheres 
differ. 

Speech  involves  both  sensory  and  motor  areas  of  the  cortex. 
Nerve-impulses,  reaching  the  sensory  areas,  affect  consciousness. 
Through  the  senses  of  hearing,  sight,  or  touch,  certain  disturb- 
ances in  the  medium  external  to  the  nervous  system  are  able  to 
arouse  in  the  sensory  areas  the  idea  of  words.  Any  permanent 
interruption  of  impulses  to  the  sensory  areas  will  result  in  deaf- 
ness,  blindness,  or  touch-ausesthesia.     The  portion  of  the  brain 


sr/:i:<n   m'iiasia.  203 

where  the  perception  otwonlt*  occurs  i.s  connected  with  an  associa- 
tion-centre, in  this  case  the  .'<pet'ch-rriitrr  located  in  the  posterior 
portion  of  the  third  frontal  convolution  of  the  left  hemisphere. 
From  this  reirion  pat  lis  run  to  various  motor  areas  of  ilie  hrain, 
tt>  the  corpus  callosum,  and  thus  to  the  opposite  hemisphere,  and 
to  the  internal  capsule.  I^esions  of  purely  motor  areas  or  paths 
ressult  in  a  loss  ot'  c.xjjression  ihrouirh  paralysis  of  the  neccssarv 
muscles.  The  effects  |)roduced  l»y  an  interruption  of  the  impulse 
along  its  incoming  or  outgoing  [»ath  arc  easily  understood.  When, 
however,  a  lesion  occurs  witliin  the  central  nervous  system  in- 
volving any  of  the  paths  required  in  speech,  the  results  are  more 
com|)licateil.  Lesions  of  sensory  areas  give  rise  to  .ieimory  ajthu.'^'a. 
When  these  are  situated  in  the  occipital  region,  there  results  an 
inability  to  form  a  comprehension  of  written  language.  Words 
are  seen,  hut  are  not  understo^td.  This  is  known  as  nhwin  or 
u'ord-bliiiilnt'iix.  In  this  case  spoken  language  is  readily  under- 
stood. Similarly  there  may  he  no rd-deafii €■■<■<,  when  written  lan- 
guage is  understood,  but  spoken  language  becomes  a  mere  series 
of  noises  without  meaning.  The  lesions  in  this  case  exist  in  the 
first  and  second  temporal  gyri  and  in  the  gyrus  supraniarginalis. 
A  destruction  of  the  paths  connecting  the  auditory  centre  with 
the  speech-centre  would  cause  word-deafness.  In  alexia  there  is 
always  an  inal)ility  to  write. 

Motor  (ij}Ji(i.'<i(i  may  consist  in  loss  of  the  power  to  speak  words 
or  to  write  words  intelligently.  When  the  lesion  involves  Broca's 
centre  the  mu.^cles  of  articulation  are  not  paralyzed.  SuclT 
patients  may  laugh,  smile,  and  vary  their  voice  so  as  to  indicate 
their  emotions.  They  may  understand  what  they  hear  and  read. 
Memory  is  not  necessarily  affected.  The  perception  of  words  is 
not  lost,  but  there  is  an  iMa])ility  to  express  words.  This  is  known 
as  aphemid.  The  loss  of  the  power  to  write  words  is  called 
agraphia.  Both  may  exist  together  or  aphemia  may  exist  without 
agraphia.  In  the  latter  condition  the  patient  cannot  speak  intel- 
ligently, owing  to  a  lesion  involving  fibres  which  connect  the 
speech-centre  with  the  motor  apparatus.  Writing  is  possible, 
however,  because  the  paths  connecting  the  sjieech-centre  with  the 
centre  governing  the  movements  of  the  hand  are  not  injured. 

An  inability  to  recall  words  is  known  as  amiw.ila.  Such 
patients  can  repeat,  upon  hearing  them,  wonls  which  before  they 
had  forgotten,  wlii<'h  is  not  true  in  motor  a|)ha>ia. 


2U4  CENTRAL  NERVOUS  SYtiTEM. 


QUESTIONS   ON   CHAPTER  XII. 

How  may  the  central  nervous  system  be  divided  ? 

What  is  a  neurone  ? 

What  is  the  length  of  the  longest  axones  ? 

What  are  collaterals  ? 

How  do  the  branches  of  nerve-cells  and  collaterals  end? 

By  what  means  are  impulses  transmitted  from  one  neurone  to  another? 

What  is  the  function  of  the  nervous  system  ? 

What  are  afferent,  efferent,  and  centi-al  neurones  ? 

What  is  a  reflex  act? 

What  is  shock  ?     How  is  it  produced  ? 

Describe  the  path  of  a  simjjle  reflex. 

Discuss  a  reflex  act  involving  consciousness. 

Discuss  the  spread  of  an  impulse  iu  the  cord. 

What  is  the  latent  period  of  a  reflex  act? 

How  is  it  affected  by  an  increase  in  the  strength  of  the  stimulus? 

Discuss  the  summation  of  stimuli  in  the  cord. 

What  is  the  smallest  number  of  segments  that  can  produce  a  reflex  in  the 
frog  ? 

How  is  the  cord  modified  as  the  animal  ascends  in  the  scale  of  development  ? 

Name  some  of  the  reflexes  found  in  man. 

Why  is  it  that  many  reflexes  uncontrolled  in  children  are  brought  under 
the  will  later  in  life  ? 

Discuss  the  diflTusion  of  impulses  in  the  cord. 

What  are  preganglionic  and  postganglionic  fibres? 

Discuss  the  cause  of  tone  of  the  body. 

How  are  spinal  reflexes  normally  modified  ?    Give  experimental  proof. 

Stimulation  of  the  cortical  areas  controlling  the  flexors  produce  what  effect 
upon  the  extensors? 

How  do  voluntary  responses  differ  from  reflexes  ? 

Give  in  detail  the  afferent  path  of  impulses  from  the  skin  to  the  cortex. 

What  cranial  fibres  have  the  same  course? 

How  are  pathways  in  the  nervous  system  determined  ? 

Describe  the  degeneration  following  section  of  the  posterior  spinal  nerve- 
roots. 

What  proof  is  there  that  vasomotor  impulses  pass  through  the  lateral  tracts 
of  the  cord  ? 

Give  the  percentage  of  impulses  passing  over  the  posterior  and  lateral 
columns. 

What  path  do  impulses  from  muscles  and  tendons  take  ? 

What  is  the  path  of  dermal  impulses? 

Describe  the  effects  of  hemisection  of  the  cord. 

What  effect  in  general  have  impulses  when  they  reach  the  cortex  ? 

What  is  the  result  of  stimulating  certain  areas  of  the  cortex  ? 

What  is  the  direction  of  the  fibres  tliat  leave  the  cortex  ?     Give  proof. 

Give  in  detail  the  path  taken  by  motor  fibres  from  the  cortex  to  the  mus- 
cles. 

What  degeneration  follows  unilateral  lesion  of  the  motor  areas  of  the  cortex  ? 

Wliat  is  the  relation  of  the  size  of  the  cortical  motor  areas  to  the  muscles 
they  control? 

How  may  each  motor  area  be  divided? 

Are  motor  areas  purely  motor  ? 

Name  the  principal  sensory  areas.     Give  their  location. 


QrESTinys  n\  rjT.\pTi:n  xir.  'iO") 

Wlial  :irc  as.s(ifiatioii-(itirc's? 

Wlial  is  till-  liitKiioii  of  iissdciiitidii-fibri's? 

What  ari"  lat('ii(  areas?     Wlicrt' loralcd  V 

Wliat  symptoms  follow  li-sioiis  of  tlic  frontal  areas? 

What  is  tile  I'uiielioii  of  the  cerehnitn  ? 

(live  the  results  of  tin-  removal  of  the  eerehrimi. 

What  is  the  fiiiutioii  of  tlie  ctTehelliiin  ? 

Give  the  results  of  removal  of  the  eerehelliim. 

What  symiiloms  follow  seetioii  of  the  commissural  lihresof  the  corebellum? 

What  are  the  forced  movements  tliat  follow  injury  to  the  eerehelliim? 

Discuss  the  function  of  the  thalamus.  Name  lilires  that  connect  it  with 
other  parts  of  the  hniin. 

What  symptoms  follow  lesions  of  thei-rura? 

What  are  the  functions  of  the  iinailrijiemina  ? 

What  symptoms  follow  lesions  of  the  ([uailriyeniina  ? 

What  are  the  functions  of  the  iiieduUa? 

Discuss  the  resultsof  division  of  the  spinal  cord. 

What  is  the  behavior  of  a  frog  whose  brain  has  l)een  destroyed  with  the 
COnl  left  intact? 

Wiiat  is  the  behavior  of  such  an  animal  when  only  tlie  lieniisplieres  hav*- 
been  remove(l  ? 

Discuss  the  function  of  each  of  the  cranial  nerves. 

What  is  the  path  of  the  fibres  of  tlie  first  cninial  nerve? 

What  is  the  jiatli  of  tlie  tibres  of  the  second  cranial  nerve? 

What  syni])tonis  result  iVom  jiaralysis  of  the  third  nerve? 

What  .symiitonis  result  from  paralysis  of  the  fourth  ? 

Discuss  the  path  of  the  fibres  of  the  fifth. 

What  is  the  result  of  .section  of  the  seventh? 

Discuss  the  jiath  of  the  tibres  of  the  cochlear  portion  of  the  eighth  nerve. 

What  is  the  path  of  tlie  vestibular  fibres  of  tlie  eighth? 

Where  are  the  cells  of  tlie  fibres  r)f  the  ninth  located  ? 

Discuss  the  functions  of  the  tenth. 

What  symptoms  result  from  section  of  the  twelfth? 

Explain  fieiieral  fatigue. 

How  is  the  inlnieranial  pressure  regulated? 

What  can  be  said  of  the  nietabolism  of  brain-cells? 

What  is  the  cause  of  sleep?     Discu.ss  sleep. 

Discuss  hypnotism. 

What  is  meant  by  the  knee-jerk? 

(live  the  evidence  for  regarding  the  knee-jerk  a  reflex  act. 

(live  the  evidence  that  knee-jerk  is  not  a  reflex  act. 

Define  nerve-centre  and  association-centre. 

What  is  meant  by  alexia  and  agraphia? 

In  what  ways  are  apheniia  and  agraphia  produced? 

What  is  amnesia? 

Distinguish  amnesia  from  motor  ajihasia. 


206 


THE  SPECIAL  SENSES. 


CHAPTER   XIII. 

THE  SPECIAL  SENSES. 
SIGHT. 

The  eye  is  a  special  orgau  by  uieans  of  which  certain  rhythmic 
disturbances  of  the  ether  atfect  consciousness  and  produce  the  sen- 
sation of  light.  Among  other  functions  that  the  eye  serves  are  the 
determination  of  color,  of  distance,  and  of  form.     It  consists  of 


Horizontal  section  of  the  riglit  eyeball  (Collins  and  Rockwell):  1.  optic  nerve; 
2,  sclerotic  coat ;  3,  cornea  ;  4,  canal  of  Schlemm  ;  5,  choroid  coat :  6,  ciliary  muscle  ; 
7,  iris;  8,  crystalline  lens;  9,  retina;  10,  hyaloid  membrane;  11,  canal  of"  Petit;  12, 
vitreous  body. 

various  adjustable  refracting  media,  by  means  of  which  the  rays 
of  light  are  focused  properly  on  the  retina,  and  of  various  mus- 
cles and  accessory  structures  by  means  of  which  the  eye  is  moved 
in  different  directions  and  is  protected. 


S  ft;  I  IT. 


'jo; 


Tlir  iniisr/m  nf  (hr  n/f  scrvr  lo  move  tlie  ('yel)all  lliroii^'-li  \vi<le 
aii;.^l('f>  ill  all  directions.  W'licii  tlic  (ixia  of  risimi  points  straijrlit 
ahead,  the  eye  is  in  the  prliiKiri/  position.  If  it  moves  iVoiii  this 
position,  so  that  the  axi.s  of  vision  rotates  either  ahoiit  the  trans- 
verse or  vertical  axis,  then  the  eye  is  in  a  nccutidar;/  position.  All 
other  positi«)ns  are  called  tertian/.  In  order  to  understand  clearly 
the  nature  of  the  ima{?e  received  by  the  eye,  it  is  only  necessary  to 
review  the  images  cast  by  a  convex  lens.  If  a  double-convex  lens 
is  taken  and  the  imajic  formed  by  a  luminous  object  is  noted,  it  is 
seen  that  it  is  an  inverted  imaffe  at  the  jioiiit  of  focus  (jf  the  lens 
if  the  luminous  object  is  {)laced  at  a  distance.  Keferriii<r  to  this 
fiirure,  it  will  be  .seen  that  the  rays  oriLnnatinir  at  A  will  be  twice 
refracted,  once  by  the  lens  as  they  enter  it  and  aji;ain  as  they  leave 
it,  so  that  all  rays  from  A  reachintr  the  lens  are  joined  at  ".     The 


Viu.  48. 


l"iirniati<in  i>l'  iiiuitrc  I'V  omivox  Ions. 

same  is  true  for  B  and  b.  Therefore  a  screen  j)laced  at  focus,  F, 
will  receive  an  inverted  image,  ob,  of  the  luminous  object  AH. 
If  the  lens  were  more  convex,  the  imaLre  would  be  formed  nearer 
the  lens;  if  the  lens  were  flatter,  the  ima<re  wouhl  fall  further 
from  the  lens.  Again,  on  the  other  hand,  if  the  image  is  to  be 
formed  at  a  definite  spot,  the  further  the  object  is  from  the  lens  the 
Hatter  the  lens  must  be  ;  and  vice  versa,  the  nearer  the  object  the 
more  curved  the  lens  must  be.  With  a  double-convex  lens  the 
image  formed  is  real,  inverted,  and  on  the  opposite  side  of  the  lens 
from  the  object.  The  crystd/line  /ens  is  a  double-convex  lens,  and 
obeys  the  laws  ju.st  described  for  other  lenses.  In  addition,  there 
are  other  refracting  media  in  the  eye — the  eoriira,  the  nqiirom^,  and 
the  ritreoits  hiimorn.  The  crystalline  lens  is.  however,  the  most 
important,  as  it  possesses  the  power  by  virtue  of  the  ci/iary  mulch's 
of  incrcasin<c  or  diminishing  its  currafKre. 


208  THE  SPECIAL  SENSES. 

By  accommodation  is  meaut  the  power  of  the  crystalline  lens  to 
change  its  amount  of  curvature,  so  as  to  throw  the  image  of  an 
object  in  exact  focus  on  the  retina  whether  the  object  be  near  or  far 
from  the  lens.  At  the  same  time  the  pupil  is  expanded  or  con- 
tracted to  admit  the  necessary  amount  of  light.  Thus,  if  an  object 
be  near  the  eye,  in  order  to  produce  a  sharp  image  the  lens  is  more 
curved,  owing  to  the  contraction  of  the  ciliary  muscle,  and  the  pupil 
is  contracted.  If,  on  the  other  hand,  the  object  be  on  the  horizon, 
the  ciliary  muscle  relaxes,  the  lens  is  flatter,  and  the  pupil  is 
dilated.  Accommodation  is  an  example  of  a  voluntary  act  brought 
about  by  the  action  of  the  unstriped  fibres  of  the  ciliary  muscle. 
The  fact  that  most  people  must  be  assisted  by  visual  sensations 
does  not  alter  the  fact  that  it  is  the  result  of  the  will.  The  nervous 
path  of  accommodation  is  through  the  anterior  part  of  the  nucleus 
of  the  third  nerve  in  the  floor  in  the  third  ventricle,  the  anterior 
bundle  of  the  uerve-root,  the  third  nerve,  the  lenticular  ganglion, 
and  the  short  ciliary  nerves. 

Atrojyiii  paralyzes  and  physostigmin  stimulates  the  ciliary  mus- 
cle. Associated  with  accommodation  for  near  vision  there  is, 
besides  the  contraction  of  the  pupil,  a  convergence  of  the  axes  of 
the  eyes.  The  farthest  point  from  the  eye  at  which  an  object  can 
be  distinctly  seen  is  called  the  far-point,  and  the  nearest  point  of 
distinct  vision  is  the  near-point,  while  the  distance  between  near- 
point  and  far-point  is  the  range  of  accommodation.  The  near- 
point  is  the  shortest  focus  of  the  crystalline,  and  is  usually  about 
five  or  six  inches. 

Emmetropia  is  the  normal  eye — that  is,  an  eye  in  which  parallel 
rays  or  rays  from  objects  at  a  distance  are  focused  upon  the 
retina  without  an  effort  of  accommodation.  Such  a  distance  for 
practical  purposes  is  considered  to  be  any  point  beyond  twenty 
feet.     Absolutely  emmetropic  eyes  are  not  common. 

Myopia,  or  near-sight,  is  the  term  applied  to  an  eye  in  which 
the  rays  from  a  distance  are  focused  in  front  of  the  retina  and 
the  image  is  blurred.  Such  an  eye  is  permanently  focused  for 
near  objects  (Fig.  49). 

Myopia  is  produced  in  two  ways — by  the  anteroposterior  diam- 
eter of  the  eye  being  too  great,  or  by  the  convexity  of  the  lens 
being  exaggerated.  In  either  case  the  focus  of  the  lens  will  fall 
in  front  of  the  retina.  The  first  condition  is  essentially  a  con- 
genital defect,  whereas  too  great  a  convexity  of  the  lens  may  be 


siaifT. 


209 


either  congenital  or  (he  re><ult  of  disease.  Myopia  is  correc'tcil  hy 
the  use  of  ii  concave  lens,  which  diverges  llie  rays  and  in  this 
way  preveutti  their  coming  to  a  focus  too  soou. 


Fig.  49. 


Myopic  eye. 

Hjrpermetropia,  or  far-sight,  is  the  reverse  of  myopia  (Fig.  50). 
In  this  cMsi'  I  lie  antcroi)osterior  axis  of  the  eye  is  too  short,  or 
else  there  is  an  al)iiorinaI  flattening  of  the  lens  which  does  not 
allow  accommodation  for  near  vision.  The  result  is  that  the 
image  of  an  object  near  by  is  focused  behind  the  retina  ;  but 
objects  at  a  distance  are  clearly  seen. 

Hypernietropia  is  corrected  by  the  use  of  a  convex  lens,  and  the 
convexity  cannot  be  in(!rensed  for  near  vision  which  adds  to  the 
refractive  power  of  the  eye. 

Frr;.  -50. 


Hypermetropic  eye. 


Presbyopia  is  defective  vision  due  to  the  loss  of  power  in 
advanced  years.  The  efaaflcity  of  the  Ien.><  becomes  less,  and  the 
convexity  cannot  be  increa.«ed  for  near  vision.  The  ciliary  nuis- 
clc  may  also  bo  weaker  and  aid  in  the  production  of  the  error. 

Astigmatism  is  a  delect  in  the  vision  due  to  irrcLndarity  in  the 
globe  of  the  eye  whereby  the  diameter  in   one  plane  is  greater 

14— Phys. 


210  THE  SPECIAL  SENSES. 

than  in  another.  Thus  the  cornea  or  the  retina  may  be  an  uneven 
surface  and  the  image  focus  definitely  in  one  part  and  falsely  in 
another.  In  this  condition  vertical,  variously  oblique,  and  hori- 
zontal lines  are  not  seen  with  equal  distinctness.  Astigmatism  is 
corrected  by  the  use  of  cylindrical  or  prismatic  glasses,  which 
have  to  be  accurately  adapted  to  the  needs  of  each  case.  This 
error,  if  serious,  usually  accompanies  other  defects  of  vision. 

Diplopia  is  the  condition  which  results  from  a  want  of  liarmony 
in  the  eyes,  so  that  the  image  of  each  eye  is  perceived  separately 
— that  is,  two  images  are  seen.  Diplopia  is  caused  commonly  by 
paralysis  or  spasm  in  one  of  the  lateral  straight  muscles,  which 
results  from  a  want  of  harmony  in  the  eyes.  If  the  eyes  are 
turned  so  that  the  axes  of  vision  separate,  the  condition  is  known 
as  external  strabismus,  or  squint;  if  the  axes  are  crossed,  the 
result  is  internal  strabismus,  or  cross-eye. 

When  a  pencil  of  rays  falls  on  a  spherical,  refracting  surface, 
those  at  the  periphery  of  the  surface  will  be  refracted  more  than 
those  which  lie  near  the  axis,  and  will  come  to  a  focus  sooner. 
This  phenomenon  is  known  as  spherical  aberration,  and  exists  also 
as  an  imperfection  in  the  eye,  where  it  is  corrected  largely  by  the 
greater  refractive  index  of  the  centre  of  the  lens,  and  partly  as 
well  by  the  fact  that  the  iris  cuts  oif  the  peripheral  rays. 

Contraction  or  dilatation  of  the  pupil  is  a  reflex  act,  and  the 
afferent  impulse  is  carried  through  the  optic  nerve,  while  the  motor 
impulse  comes  through  the  third  cranial  nerve,  acting  from  a 
centre  just  beneath  the  aqueduct  of  Sylvius  and  the  corpora 
quadrigemiua.  The  increase  in  the  amount  of  light  that  comes  to 
the  retina  causes  a  contraction  of  the  pupil,  and  a  decrease  is  fol- 
lowed by  a  dilatation.  The  pupil  is  controlled  also  by  fibres  of 
the  sympathetic  and  fifth  nerve  which  connect  with  the  ciliary 
ganglion.  Drugs  are  active  in  controlling  the  action  of  the  iris, 
Atropin  both  locally  and  internally  dilates  the  pupil ;  o/)i«m  taken 
internally,  and  eserin  applied  locally,  contract  it. 

If  in  obtaining  an  image  of  an  object  through  a  double  convex 
lens  the  lens  be  too  large,  there  will  be  seen  around  the  image 
formed  a  halo  of  prismatic  colors.  This  is  called  achromatism, 
and  is  produced  by  an  tmequal  refraction  of  light-rays  by  the 
peripheral  portions  of  the  lens.  The  unequal  refraction  results 
in  a  dispersion  of  the  light,  so  that  it  is  broken  up  into  the 
primary  colors.     This  defect  is  remedied  by  putting  a  shutter  in 


siniiT.  211 

front  of  the  lens,  and  so  liinitini,'  the  entranre  of  li{;lit  to  the 
(vntral  portions  of  tlie  lens,  where  the  index  of  refraction  is  con- 
stant. In  the  eye  the  iris  acts  as  a  shutter,  thus  rnakinj^  the 
image  achromatic,  hut  in  some  defective  eyes  where  there  is  con- 
siderahle  fault  in  the  focus  of  the  image  on  tiie  retina  a  visii)le 
band  of  color  appears. 

Under  certain  conditions  a  nuiid)er  of  ohjects  lying  within  the 
eye  itself  become  visible.  Of  these  intraocular  images,  the  most 
common  are  known  as  musca'  vo/ita)itrs.  These  are  in  the  form 
of  beails,  streaks,  or  patches.  They  have  an  independent  motion, 
which  is  increased  l)y  the  movements  of  the  eye.  They  are  of 
greater  s|)ecitic  gravity  than  the  medium  in  which  they  are  found, 
and  are  suj)posed  to  l)e  the  remains  of  the  ('m/jrijo)iic  structure  of 
the  vitreoua  body. 

Under  normal  conditions  the  pupil  appears  as  a  black  spot. 
The  reason  for  this  is  that  the  source  of  light  and  the  retina  lie  in 
conjugate  foci,  so  that  any  light  which  escapes  absorption  by  the 
retinal  pigment  is  reflected  hack  whence  it  came.  Therefore  the 
eye  of  an  ol)server  who  views  it  from  another  direction  will  see  no 
light  coming  from  it.  By  means  of  an  ophtlialmoscope,  however, 
a  strong  light  is  thrown  into  the  fundus  of  the  eye,  which  upon 
reflection  is  viewed  by  an  observer  through  an  opening  iu  the  re- 
flector. The  fundus  is  seen  to  have  a  reddish  background  in 
which  the  retinal  vessels  are  visible.  The  most  important  struct- 
ures are  the  ro(h  and  cones.  They  are  closely  packed  on  the 
outer  surface  of  the  retina,  the  rods  over  the  greater  part  of  the 
retina  being  the  more  numerous.  They  are  cylindrical  bodies  of 
a  transparent  substance  placcvd  parallel  to  one  another  and  per- 
pendicular to  the  surface  of  the  eyeball.  The  cones,  which  are 
modifications  of  the  rods,  are  very  similar  to  the  latter,  but  do 
not  reach  the  same  level.  These  structures  are  connected  more 
or  less  directly  with  the  fibres  of  the  optic  nerve.  Where  this 
nerve  enters  the  retina,  a  little  to  the  inner  side  of  the  most  pos- 
terior point  of  the  eyeltall,  there  are  no  rods  or  cones,  so  that  an 
image  focused  at  tliis  point  will  be  followed  by  no  ])erception. 
This  ])oint  is  called  the  hliiid  xpot.  If  the  left  eye  is  covered  and 
the  right  directed  steadily  upon  the  cross  in  Fig.  51,  the  circular 
spot  will  be  visible  at  the  same  time,  though  less  distinctly.  As 
the  book  is  moved  slowly  backward  and  forward,  a  point  will  be 
found  at  which  the  round  spot  disappeai-s,   reappearing  as  the 


212  THE  SPECIAL  SENSES. 

book  is  held  nearer  or  farther,  or  as  it  is  inclined  in  either  direc- 
tion and  the  image  is  carried  from  the  blind  spot. 

At  the  exact  centre  of  the  retina — that  is,  the  most  posterior 
point  of  the  eye — there  is  a  small  yellow  area  (jnacula  lutea)  with 
a  central  depression  (fovea  centralis).  Here  none  of  the  fibres  of 
the  optic  nerve  are  to  be  found,  but  a  great  increase  in  the 
number  of  cones  as  well  as  an  increase  in  their  size.  If  the  object 
looked  at  is  focused  directly  upon  the  macula  lutea,  the  image  is 
seen  with  greatest  clearness.  In  everyday  life  images  are  received 
upon  the  macula  lutea,  and  rays  of  light  entering  the  eye  at  an 
angle  are  focussed  on  some  other  part  of  the  retina,  and  are  not 
defined  so  clearly. 

A  retina  which  has  been  protected  from  the  light  for  a  time  has 
a  purplish-red  color,  due  to  a  coloring-matter  termed  visual  purple. 
This  is  confined  to  the  outer  portions  of  the  rods  and  does  not 

Fig.  51. 


reach  the  cones.  It  is  bleached  by  light,  but  restored  by  the  pig- 
ment epithelium.  The  retina  of  a  rabbit  may  be  impressed  with 
an  image  focused  upon  it  and  then  treated  with  a  4  per  cent, 
solution  of  alum,  which  "fixes"  it  and  prevents  the  restoration 
of  the  visual  purple.     Such  a  picture  is  called  an  optogram. 

Vibrations  of  the  ether  form  the  normal  stimulus  for  the  retina, 
the  rods  and  cones  of  which  form,  perhaps,  the  only  structures  of 
man  that  can  supply  the  necessary  conditions  for  the  transfor- 
mation of  radiant  energy  into  the  energy  of  a  nerve-impulse. 
The  ether- vibrations  vary  widely  in  their  frequency,  and  only 
certain  ones  are  capable  of  affecting  the  eye.  The  impulses  they 
generate  pass  to  the  brain  by  way  of  the  optic  nerves,  giving  the 
sensation  of  light. 

If  the  optic  nerves  are  examined  in  a  superficial  manner,  they 
will  be  seen  to  leave  each  eye  and  pass  backward  through  the 


SIGHT. 


'2i:i 


optic  foramina  until  they  reach  tlie  body  of  the  sphenoids.  Here 
they  cross  one  another  in  tlie  form  of  an  X  (optic  chiasm;,  the 
fibres  intermingling,  and  the  right  nerve  apparently  i)assing  over 


¥ui.  52. 


Left  Eye 


Rhjht  Eye 


Optic  radio 


Optic  radiation 


Cortex  of  occipital 
lobe  witli  cortical  cells 


1,  external  geniculate  body;  2,  pulvinar:  S,  anterior  quadripeininate  body;  4,  inter- 
nal geniculate  body  ;  •'),  citniniissurc  of  <;ud(U'n.     iCoUiiis  ami  Hockwell.) 


to  the  left  side  and  the  left  nerve  to  the  right  side.  The  posterior 
limhs  of  the  X  jiass  backward,  and  are  called  the  optic  tracts. 
The  optic  tract.s  in  their  course  curve  around  the  crura  cerebri  to 


214  THE  SPECIAL  SENSES. 

terminate  in  the  ganglion-cells  of  the  pulvinar,  anterior  quadri- 
gemina,  and  external  geniculate  bodies.  From  these,  ganglion- 
cell  fibres,  called  the  optic  radiations,  pass  backward  to  terminate 
in  the  ganglion-cells  of  the  cortex  of  the  posterior  part  of  the 
occipital  lobes.  A  closer  examination  of  the  optic  nerves  will 
show  that  each  consists  of  two  distinct  bundles  of  fibres  laterally 
placed.  The  inner  set  of  fibres  conies  from  the  inner  half  of  the 
retina ;  the  outer  bundle  comes  from  the  outer  half  of  the  retina.  If 
these  bundles  are  traced  to  the  optic  chiasm,  it  is  noted  that  the 
inner  bundles  decussate  and  pass  to  the  opposite  side  of  the  brain. 
Thus  the  left  pulvinar,  left  anterior  quadrigeminate,  and  external 
geniculate  bodies  receive  fibres  from  the  inner  half  of  the  right  eye, 
and  from  the  outer  half  of  the  left  eye.  The  commissure  of 
Gudden,  which  connects  the  internal  geniculate  bodies,  probably 
plays  no  part  in  vision.  When  an  image  is  properly  received  on 
the  retina,  it  excites  the  rods  and  cones  to  activity.  When  the 
impulses  reach  the  basal  ganglia,  the  sensation  of  light  is  not  aroused. 
Light  is  not  perceived  until  the  impulses  reach  the  cortex  of  the 
cerebrum.  The  pulvinars,  the  external  geniculate  bodies,  and  the 
anterior  quadrigemina  form  the  j^rhnary  vision  centre. 

The  character  of  the  sensations  aroused  depends  upon  three 
modifications  of  light : 

1.  Color,  which  depends  upon  the  rate  of  vibration  of  the  ether- 
waves. 

2.  Intensity,  which  depends  upon  the  energy  of  the  vibrations. 

3.  Saturation,  which  depends  upon  the  amount  of  white  light 
mixed  with  light  of  one  wave-length. 

It  is  easily  demonstrated  for  man  that  luminosity  is  recognized 
more  easily  than  color,  and  this  probably  holds  true  for  all  organ- 
isms. Colored  objects  appear  colorless  when  the  light  is  too  feeble, 
and  if  the  light  is  increased  in  intensity  the  colors  appear,  but  as 
it  becomes  too  strong  there  is  a  tendency  for  all  colors  to  pass  into 
white.  This  is  most  noticeable  in  the  yellow.  DiflTerent  regions 
of  the  retina  vary  also  in  their  power  to  distinguish  colors.  Red 
is  lost  at  a  short  distance  from  the  macula  lutea,  while  the  violet 
is  lost  only  at  the  borders  of  the  retina. 

Stimulation  of  the  retina  is  followed  normally  by  a  latent  period, 
then  by  a  period  during  which  the  effect  of  the  excitation  reaches 
a  maximum  ;  from  the  maximum  there  is  a  slow  decline  in  the 
effect,  which  is  analogous  to  fatigue,  and  when  the  stimulation  has 


siC'iiT.  215 

ceased  there  is  an  after-effect  which  sh)\vly  passes  away.  When  a 
very  hri<rht  uhject  is  looked  at  for  some  time,  the  impres-iion  upon 
the  retina  hists  for  a  eonsi(k'rahle  interval  after  the  excitation  has 
ceased.  This  is  called  the  positive  after- ima(/e.  Both  form  and 
color  are  visible.  The  latter  generally  passes  through  a  series  of 
colors — green,  blue,  violet,  purple,  and  red — before  it  disappears. 
The  iwyatiir  after-imatje  de})ends  upon  fatigue  of  the  retina,  and 
differs  from  tlu'  positive  after-image  in  that  its  color  is  tiie  comple- 
mentary of  that  of  the  object.  The  efi'ect  produced  by  an  object 
upon  the  ri'tina  depends  in  part  u])on  the  amount  it  has  been 
fatiguetl  by  previous  impressions.  This  makes  the  field  of  vision 
appear  ilarker  near  a  light  area  and  lighter  near  a  dark  area  than 
it  really  is,  while  the  color  is  so  modified  by  the  neighboring  field 
that  it  appears  the  complementary  of  the  latter. 

Ordinary  xchite  liyht,  if  decomposed,  is  resolved  into  the  seven 
primary  colors — violet,  indigo,  blue,  green,  yellow,  orange,  and 
red.  Each  of  these  primary  colors  has  a  different  wave-length. 
Colors  other  than  the  seven  primary  colors  are  the  result  of  the 
mixture  of  two  or  more  of  the  primary  colors  in  various  propor- 
tions. Nothing  is  known  of  the  manner  in  which  the  rods  and 
cones  are  made  to  vibrate  by  ordinary  images,  nor  as  to  the  nature 
of  the  process  by  which  the  different  color-effects  are  conveyed  by 
the  optic  nerve.  The  different  color  theories  assume  that  there  are 
different  substances  in  the  retina  cajialile  of  responding  to  different 
wave-lengths  of  light  ^comparable  to  a  photochemical  process). 
Reil.  green,  and  violet  are  the  fundamental  colors  and  all  others 
can  l)e  made  by  coml)inations  of  these  three.  Working  on  this  basis. 
Young  and  Hrlmholtz  assumed  three  chemical  substances  in  the 
retina  capable  of  responding  to  the  three  fundamental  colors. 
Hering  assumed  three  substances  corresponding  res|)ectively  to 
white  or  black,  red  or  green,  and  yellow  or  blue  light.  In  this 
theory  the  white,  red,  and  yellow  rays  are  kataliolic  in  their  effects 
on  their  imlividual  recipient  substances,  while  black  (absence  of 
light),  green,  and  blue  are  anabolic,  thus  having  an  antagonistic 
effect.  Mrx.  Franklin  assumes  in  lier  theory  that  in  early  life  the 
eye  posseSvSes  no  color-perception,  l)ut  merely  the  power  of  perceiving 
luminosity — i.  e.,  distinguishing  between  white  or  black.  The  sulv 
stance  responding  to  luminosity  is  called  gray-perceiving.  As  the 
development  jirogresses,  some  of  the  gray  is  differentiated  into  a 
blue  and  a  yellow-perceiving  substance.     The  yellow-perceiving 


216 


THE  SPECIAL  SENSES. 


substance  is  still  further  difierentiated  in  the  course  of  development 
into  a  red-  and  a  green-perceiving  substance  ;  thus — 

Gray. 


Blue. 


Yellow. 


Green. 


Red. 


Many  objections  have  been  raised  against  each  of  these  theories, 
but  Mrs.  Franklin's  is  so  far  the  best,  and  explains  more  readily 
the  causes  of  color-blindness.  According  to  the  theories  of  Helm- 
holtz  and  Hering,  color-blindness  is  due  to  an  absence  of  one  or 
more  of  the  fundamental  color-perceiving  substances.  Mrs.  Frank- 
lin's theory  assumes  a  lack  of  full  development  or  complete  absence 
of  development  of  gray  substance.  If  the  development  should  cease 
after  the  blue-  and  yellow-perceiving  substances  have  been  formed, 
the  individuals  would  be  capable  of  distinguishing  the  blues  and 
yellows,  but  could  not  recognize  reds  and  greens.  Clinically  such 
cases  often  are  met  with.     Males  are  far  more  likely  to  be  color- 

FiG.  53. 


Diagram  of  three  primary  color  sensations  (Foster) :  1  is  the  so-called  "  red,"  2, 
"green,"  and  3,  "violet"  primary  color  sensation.  R,  0,  Y,  etc.,  represent  the  red, 
orange,  yellow,  etc.,  color  of  the  "spectrum,  and  the  diagram  sliows  by  the  height  of 
the  curve  in  each  case,  to  what  extent  the  several  primary  color  sensations  are 
respectively  excited  by  vibrations  of  different  wave-lengths. 


blind  than  females  (16  to  1).     Only  1  woman  in  400  is  color- 
blind.    The  reason  for  this  is  partly  at  least  that  the  development 


SIGHT.  217 

of  the  gray-perceiving  substance  is  favored  by  practice  and  color 
education.  Such  an  education  is  often  neglected  in  boys,  butgirl.s 
receive  sufficient  practice  often  iu  matching  colors  for  doll's 
clothing,   etc. 

The  retina  is  capable  of  judging  the  size  of  objects  in  two  <liMion- 
sions  only — /.  c,  in  the  plane  perpendicular  to  the  axis  of  vision. 
The  perception  of  didancr  is  closely  connected  willi  the  fact  tiiat  the 
size  of  the  image  f  )riued  upon  the  retina  varies  with  the  distance. 
Besides,  the  distinctness  with  which  objects  are  seen  intiuences  the 
judgment  of  distance  because  when  indistinctly  seen,  objects  are 
supposed  to  be  farther  away.  Again,  the  judgment  of  distance  is 
further  aided  by  the  sense  of  elfort  required  in  accommodation  and 
also  by  the  change  of  position  of  an  image  on  the  retina  when  the 
eye  is  mov^ed.  Tlie  latter  depends  upon  the  fact  that  the  change 
in  the  position  of  the  image  is  inversely  proportional  to  the  distance 

Fio.  54. 


ED 


Illustration  nf  irradiatiun.     (McKcndrick.) 

of  the  objects.  Many  circumstances  affect  the  accuracy  of  the 
spatial  judgment  of  the  retina.  One  of  these  is  irradiation.  All 
brightly  illuminated  ol)jects  appear  larger  than  others  of  the 
same  size. 

The  illusion  of  Zi'dlner's  lines  is  due  to  the  fact  that  through 
early  association  with  right  angles  as  seen  in  all  parts  of  our  houses, 
etc.,  and  which  are  viewed  from  different  directions  so  that  they 
appear  acute  or  obtuse.  The  tendency  of  the  mind  is  therefore  to 
make  such  angles  right  angles,  so  that  acute  angles  are  overesti- 
mated while  obtuse  angles  are  underestimated.  In  Fig.  55  the 
heavy  lines  are  consequently  made  more  perpendicular  to  the  short 
cross-lines  than  is  absolutely  the  case,  which  brings  the  alternate 
ends  of  the  heavy  lines  closer  together. 

Although  there  are  two  eyes,  each  of  which  furnishes  an  im- 
pression, only  one  object  is  perceived.  In  abnormal  positions  of 
the  eye  the  two  impressions  can  be  made  recognizaI)le.     Ordi- 


218 


THE  SPECIAL  SENSES. 


narily,  therefore,  the  images  of  objects  fall  on  corresponding  points 
of  the  retina.     A  point  on  the  right  side  of  one  retina  has  its  cor- 


FiG.  55. 


Zollner's  figure  showing  an  illusion  of  direction.    (McKendrick.) 

responding  point  on  the  left  side  of  the  retina  of  the  other  eye. 
When  the  images  fall  on  corresponding  points,  they  are  blended 

Fig.  56. 


\ 

/ 

/ 

\ 

X 

B 

/ 

k 

\ 

/ 

X^ 

Illustrating  the  principle  of  the  stereoscope  and  binocular  vision. 

into  one  perception.     Binocular  vision  affords  a  method  of  judg- 
ing the  solidity  of  objects,  since  the  image  of  any  object  falling  on 


HEARiyu.  219 

one  eye  cannot  he  cxartly  like  tliat  wliifli  (alLs  on  the  otlier. 
Thus  the  j)frcc'|>tive  liicultii'.s  can  juil^e  inure  correctly  <j1'  the 
i'onn  and  distance  of  an  ohjcct. 

From  the  hiws  ot"  optics  it  is  known  tliat  the  inia^'c  formed  on 
the  retina  is  an  iiivcrtal  uikkjc  of  the  object.  Vet,  it  is  perceived 
in  its  uprijrht  position.  This  is  the  result  (»f  lifelonj:  iiahit.  A 
htii)v  sees  an  object ;  the  next  step  is  to  touch  it ;  hy  practice  the 
eliihl  iinds  out  which  is  the  top  of  the  object  through  the  touch 
perception.  Very  speedily  the  brain  learns  to  make  the  correc- 
tion. It  is  an  act  of  mental  and  not  physical  origin.  Thus, 
objects  which  are  projected  ui)on  the  left  of  the  retinal  surface 
look  to  be,  as  tiiey  really  are,  on  the  right  of  the  body  ;  and  so 
with  all  the  directions. 

Vlearnesii  of  visiun  depends  ujion  the  space  between  the  cones 
in  the  point  of  clearest  vision,  the  macula  lutea.  It  has  been 
calculated  that  an  object  must  subtend  an  arc  of  at  least  60  to  70 
seconds  in  the  field  of  vision  to  be  clearly  seen.  Such  an  object 
makes  an  image  ^^-^-^  of  an  inch  on  the  retina,  and  this  is  about 
the  distance  between  the  cones  at  the  macula  lutea.  In  order 
that  two  points  may  be  distinguished,  they  must  be  separated  at 
least  this  amount. 

HEARING. 

It  may  be  accepted  as  a  well-defined  physiologic  fact  that  the 
nervous  structures  of  the  cochlea  form  that  organ  by  which  musical 
sound  and  noise  of  all  kinds  are  converted  into  nerve-impulses. 
The  sound-waves  of  the  air,  which  originate  in  vibrating  bodies, 
are  gathered  together  by  the  concha,  carried  into  the  external 
auditory  canal,  and  vibrate  against  the  membi*ana  tympani.  The 
latter  takes  up  the  vibrations  and  transmits  them  tli rough  the 
chain  of  ossicles  to  the  stapes  in  the  fenestra  ovalis.  The  stapes 
imparts  its  motion  to  the  perilymph  of  the  vestibule  (Fig.  57). 
There  is  now  set  up  in  the  perilymjih  a  fluid  wave  that  travels  in 
all  directions.  It  passes  along  the  scala  vestibuli  to  the  apex  of 
the  cochlea,  then  through  the  aperture  of  communication  with  the 
scala  tympani  down  the  latter  until  it  expends  itself  against  the 
membrane  of  the  fenestra  rotunda.  In  its  pa.^sage  the  fluid 
vibrates  against  the  membrane  oi'  Keissner  and  the  basilar  mem- 
brane, and  this  sets  up  similar  vibrations  in  the  endolymj>h  of  the 
canalis  cochlearis.     The  llnid   wave  in  the  canalis  cochlearis  is  in 


220  THE  SPECIAL  SENSES. 

a  position  to  irritate  the  hair-cells  of  the  organ  of  Corti.  These 
cells  seem  to  be  able  to  respond  to  particular  tones  by  their  sensi- 
tiveness to  certain  rates  of  vibration.  But  the  fact  that  the 
organs  of  Corti  are  absent  in  birds  which  evidently  are  capable 
of  appreciating  musical  tones  shows  that  they  are  accessory  and 
not  absolutely  essential. 

The  branch  of  the  eighth  nerve,  having  received  its  impulses 
from  the  cells  of  the  organ  of  Corti,  transmits  them  to  the  centre 
under  the  acoustic  tubercle  in  the  floor  of  the  fourth  ventricle  ; 

Fig.  57. 


Diagrammatic  view  of  the  relative  position  of  the  parts  of  the  ear  (Chapman) : 
EM,  external  meatus ;  T?/M,  tympanic  membrane ;  Tij.  tympanum ;  M,  malleus ; 
I,  incus;  S,  stapes;  R,  round  window;  O,  oval  window;  SG,  semicircular  canal; 
U,  utriculus;  S,  sacculus ;  V,  vestibule;  SV,  scala  vestibula ;  ST,  scala  tympani; 
MC,  membranous  cochlea ;  LS,  lamina  ossea ;  Em,  Eustachian  tube ;  AN,  auditory 
nerve. 

thence  fibres  pass  by  means  of  the  trapezium  in  the  pons  to  the 
opposite  side,  and  through  the  lower  fillet  of  that  side  to  the  pos- 
terior quadrigeminal  body,  whence  by  means  of  the  brachium, 
internal  geniculate  body,  optic  thalamus,  and  internal  capsule, 
they  proceed  to  the  cortex  of  the  first  and  second  temporal  con- 
volutions. 

By  suhjeetive  hearing  is  meant  sounds  that  are  heard  distinctly 
and  yet  are  not  produced  by  physical  sound-waves  from  the 
exterior,  nor  are  they  hallucinations.  They  may  be  due  to  dis- 
turbances of  the  auditory  apparatus  or  to  abnormal  conditions  of 


SENSE  OF  EQl'ILinnirM.  221 

surrounding  organs.  Thus  huzzing  or  ringing  in  the  cjirs  may 
result  from  the  liypeneniiji  of  the  parts  and  the  increa.M-d  rush  (if 
hlood,  or  from  disease  in  the  auditory  nerve  or  some  other  portion 
of  the  apparatus.  Ilalhicinalions  are  purely  creations  of  a  <lis<»r- 
dered  brain. 

Mtiiiival  xohikIx  are  distiniruished  hy  the  mind  hy  three  faetors 
— loudness,  pitch,  and  fpiality.  Every  musical  tone  is  produce<l 
hy  a  succession  of  regular  alternate  rarefactions  and  conden.sa- 
tions  of  the  air.  It  is  their  y>cr/W/r//y  which  makes  tliem  musical, 
otherwise  they  are  known  as  noises.  The  range  of  musical  notes 
that  can  he  appreciated  by  the  hun)an  ear  is  about  .seven  octaves. 
There  are  about  oOOO  hair-cells  in  the  organ  of  Corti,  and  it  is 
easily  seen  that  this  would  allow  an  enormous  capabUity  to  <liffer- 
entiate  sounds  and  musical  tones.  This  corresponds  to  a  range  of 
from  40  to  about  4000  vibrations  per  seconil.  The  range  oi'  (tutli- 
bi/itij,  on  the  other  hand,  is  about  eleven  octaves,  or  from  16  to 
38,000  vibrations  per  second.  With  less  than  16  vibrations  per 
second  the  ear  perceives  only  separate  shocks,  while  with  more 
than  the  larger  number  the  sensation  of  sound  is  not  jiroduced. 

The  dixtiDice  and  diredion  of  Rouuda  are  not  perceived  directly, 
but  are  estimate<l  by  their  loudness  and  cpiality  condiined  with 
rea.soiiing  from  past  experience.  When  one  ear  is  totally  deaf, 
all  sounds  seem  to  originate  from  the  side  of  the  healthy  ear. 
When  the  eyes  are  clo.sed,  a  sound  directly  overhead  is  imperfectly 
localized,  but  seems  to  come  from  a  point  ahead  and  above  the 
person.  The  quality  as  well  as  the  loudness  of  the  sound  varies 
with  the  distance  from  its  source,  because  the  lower  tones  die 
away  first,  making  the  overtones  more  prominent.  This  is  taken 
advantage  of  by  voilrilnqHixfH,  who,  by  modifying  the  intensity 
and  (juality  of  the  voice,  ))roduce  an  imitation  of  the  effect  of  dis- 
tance. The  ear  is  capable  of  appreciating  very  small  intervals 
of  time;  182  auditory  impulses  j^er  second  are  heard  separately, 
while  in  the  eye  all  above  24  per  second  are  fused  together. 

SENSE  OF  EQUILIBRIUM. 

By  sense  of  equililn-iuni  or  equipoise  is  meant  a  state  of  the 
body  in  which  all  the  muscles  are  under  the  control  of  nerve- 
centres  so  as  to  resist  the  eflVct  of  gravity  whenever  nece.<.sary.  It 
is  of  the  greatest   im])ortance  to   animal.s  and   therefore  several 


222  THE  SPECIAL  SENSES. 

mechanisms  share  in  its  performance.  It  is  brought  about  by 
sensory  impulses  coming  from  many  sources,  and  the  sum-total 
of  the  sensations  involved  constitutes  the  sense  of  equilihrium. 
Every  known  sensation  probably  contributes  to  the  maintenance 
of  equilibrium,  but  certain  structures  in  the  ear,  known  as  the 
semicircular  canals,  form  the  main  source.  When  the  canals  are 
injured  in  any  way,  the  animal  sprawls  on  the  ground,  holds  its 
head  in  an  unnatural  position,  makes  peculiar  forced  movements, 
etc.  The  effect  varies  with  the  number  and  the  position  of  the 
canals  operated  upon,  and  ranges  from  simple  unsteadiness  of  gait 
to  complete  incoordination.  These  results  are  explained  as  being 
due  to  increased  or  decreased  pressure  of  the  endolymph  on  the 
cristse  acusticee  of  the  ampullae  of  the  semicircular  canals.  The 
latter  are  situated  in  the  three  dimensions  of  space,  and  rotation 
of  the  body  in  any  direction  can  be  judged  quite  accurately  as  to 
direction  and  amount.  Rapid  rotation  in  one  direction  is,  after 
its  cessation,  often  followed  by  a  sensation  of  rotation  in  the  oppo- 
site direction.  Excessive  rotation  leads  to  dizziness,  but  in  deaf- 
mutes  dizziness  is  difficult  to  produce  on  account  of  the  imperfect 
development  of  the  ears.  Diseases  which  alter  the  pressure  in 
the  canals  lead  to  vertigo  and  incoordination.  The  semicircular 
canals  in  themselves,  however,  are  not  sufficient  to  preserve  com- 
plete equilibrium. 

SMELL  AND  TASTE. 

The  special  olfactory  mucous  membrane  is  situated  in  the  upper 
part  of  the  nasal  cavity,  away  from  the  direct  current  of  the  in- 
spired air.  The  rod-cells  which  it  contains  are  connected  with 
fibres  that  are  part  of  the  olfactory  nerve  and  constitute  the  sensory 
nerve-endings.  Substances  that  excite  the  sense  of  smell  are  in  a 
fine  state  of  division  or  in  a  gaseous  state,  and  are  brought  into 
contact  with  the  rod-cells  by  rapid  but  short  inspiratory  movements. 
They  are  perceived  best  when  the  air  is  at  the  body-temperature. 
The  substance  producing  smell  is  probably  taken  into  solution  in 
the  moisture  covering  the  olfactory  membrane.  In  the  low^er 
animals  the  sense  of  smell  plays  a  very  important  part,  and  it  is 
probable  that  all  animals  give  out  characteristic  odors  by  which 
they  recognize  one  another.  The  sense  of  smell  is  therefore  highly 
developed,  which  is  not  the  case  in  man.  The  distribution  of  the 
olfactory  nerves  is  much  wider  and  the  cerebral  development  cor- 


SMELL  AND   TASTE.  223 

respondingly  greater  in  some  animals  than  is  the  case  in  man, 
wliere,  however,  the  range  ofsusceptil)ility  is  wider.  The  variety 
of  odors  and  tlie  very  minute  quantity  of  the  substance  required  to 
produce  smell  are  wonderful.  The  most  delicate  analysis  may  fail 
to  show  traces  of  the  substances  which  can  be  appreciated  by  the 
sense  of  smell.  For  instance,  O.OUOOOOOOo  of  a  gramme  of  oil  of 
peppermint  in  1  liti-e  of  water  can  be  detected.  Some  odors,  like 
musk,  are  pleasant  perfume  to  some,  while  to  others  they  are  un- 
endurable. The  acateness  of  the  sense  of  smell  varies  in  different 
persons,  and  this  may  apply  to  certain  odors  only.  Like  the  sense 
of  touch  and  other  senses,  it  can  be  developed  by  practice.  Often 
in  cases  of  mental  disease  there  are  hallucinations  of  smell. 

The  olfactory  nerves  arise  from  a  mass  of  gray  matter  lying  be- 
neath the  anterior  lobe  of  the  brain  upon  the  cribiform  plate  of 
the  ethmoid  bone.  This  is  the  olfectory  bulb,  and  is  connected  by 
the  olfactory  tract  with  the  cerebrum.  Each  olfactory  trad  arises 
from  the  cerebrum  by  three  roots,  two  of  which  are  composed  of 
white  matter,  and  the  third  of  gray  matter.  By  these  it  is  con- 
nected with  the  olfactory  centres.  The  perceptions  of  the  olfactory 
nerve  and  of  the  nerves  of  touch  of  the  nose  often  resemble  each 
other,  and  some  stimuli  affect  both  nerves.  The  common  sensibility 
is  evoked  by  such  substances  as  are  irritating  or  acrid — ammonia 
gas  has  no  odor,  but  it  stiiuulates  the  mucous  membrane  of  the 
nose.  The  relation  between  the  two  kinds  of  perception  is  lost, 
and  the  smell  of  ammonia  or  of  alcohol  is  spoken  of  when  it  is 
not  olfactory,  but  a  sensory  perception. 

Taste. — The  sense-organs  concerned  in  taste,  the  taste-buds,  are 
located  on  the  upper  surface  and  sides  of  the  tongue,  the  anterior 
surface  of  the  palate  and  of  the  anterior  pillars  of  the  fjiuces. 
Those  of  the  posterior  third  of  the  tongue  are  connected  with  the 
glossopharyngeal  nerve,  while  those  of  the  anterior  part  of  the 
tongue  are  connected  with  the  lingual  and  chorda  tympani  nerves. 
Taste-perceptions  are  modified  by  simultaneous  olfactory  sensations, 
so  that  it  is  difficult  to  distinguish  between  an  apple  and  an  onion 
when  the  nostrils  are  closed.  The  intensity  of  taste  increases  with 
the  area  stimulated,  and  is  greatest  when  the  stimulating  substance 
is  at  the  tem])erature  of  the  body.  Taste  depends  upon  the  con- 
centration of  the  solution.  There  is  evidence  that  the  sen.'sation 
may  be  divided  into  four  primary  ones — bitter,  sweet,  sour,  and 
salt,  with  special  nerves  and  end-organs  for  each      Thus,  the  tip  of 


224  THE  SPECIAL  SENSES. 

the  tongue  perceives  acids  acutely,  sweets  less,  and  bitter  substances 
hardly  at  all.  Saccharin  appears  sweet  at  the  tip  of  the  tongue 
and  bitter  at  the  base.  The  fungiform  papillae  scattered  over  the 
surface  of  the  tongue  were  tested  with  succinic  acid,  quinine,  and 
sugar.  Out  of  125,  27  did  not  respond  at  all,  showing  that  they 
were  devoid  of  taste-endings ;  12  reacted  to  succinic  acid  alone ;  3 
to  sugar  alone  ;  while  quinine  affected  them  all.  An  extract  of  a 
tropical  plant  has  been  found  to  paralyze  the  sense-endings  for 
sweet  and  bitter  substances.  Cocaine  abolishes  the  sensibility  of 
the  tongue  in  the  following  order  :  (1)  general  feeling  ;  (2)  bitter 
taste ;  (3)  sweet  taste ;  (4)  salt  taste ;  (5)  acid  taste ;  (6)  tactile 
perception. 

The  tongue  has  a  highly  developed  sense  of  touch,  temperature, 
pressure,  and  pain,  which  aid  the  accuracy  of  speech,  mastication, 
and  deglutition.  Some  aromatic  substances  leave  an  impression  of 
their  taste,  called  an  after-taste,  and  when  tasted  in  rapid  succession 
a  number  of  times  the  appreciation  of  their  flavor  is  lost. 

CUTANEOUS  SENSATIONS. 

A  specialized  peripheral  organ  for  the  reception  of  an  external 
impression,  an  afferent  nerve,  and  the  brain  for  the  perception 
of  the  sensation,  constitute  the  organs  for  sensation.  It  is  by  means 
of  impressions  so  received  and  conducted  to  it  that  the  mind  is  able 
to  control  the  body  and  to  take  cognizance  of  the  external  world. 
Cutaneous  sensations  include  the  sense  of  touch,  temperature,  and 
pain.  Touch  is  due  to  sensory  nerve-endings  in  the  skin  and  mu- 
cous membrane.  The  nails  and  teeth  are  peculiarly  involved  in 
the  sense  of  touch,  and  also  the  hair  in  certain  regions — e.  g.,  the 
eyelashes.  The  relation  between  the  strength  of  the  stimulus  and 
the  resulting  sensation  is  expressed  by  Weber's  law  :  "  The  amount 
of  stimulus  necessary  to  provoke  a  perceptible  increase  of  sensation 
ahvays  bears  the  same  ratio  to  the  amount  of  stimulus  already  applied." 
This  law  is  only  approximately  correct  for  small  and  for  large 
weights.  Fechner's  "  psychophysieaV  laiv  attempts  to  express  the 
relation  more  exactly  :  "  The  intensity  of  sensation  varies  with  the 
logarithm  of  the  stimulus" — i.  e.,  the  sensation  increases  in  arith- 
metical, while  the  stimulus  increases  in  geometrical  proportion. 

Different  areas  of  the  body  vary  in  their  power  of  discriminating 
pressure-differences.     The  forehead,  lips,  and  temples  appreciate 


CUTANEOUS  sp:nsations.  22r) 

ail  increase  of  .,'^  to  ^\)  ;  Ixil  tlio  head,  liiiLTtis,  and  forearm  can 
appreciate  a  stinmiu.s  only  wlicn  increasi-d  iVoni  .,'f,  to  ^\^  of  it« 
prcvions  intensity.  Wlicn  two  ecjual  \vei<,'lits  of  dilfcrent  expanse 
press  upon  the  skin,  tlic  larjriT  appears  the  heavier.  A  wei^.dit 
pressinL,^  upon  the  skin  leaves  an  (tJIcr-Hruxatioii,  so  that  the  inter- 
vals between  successive  applications  of  stimuli  to  touch-cndinfrs 
cannot  he  less  than  ,,  { ^^  of  a  second  if  they  are  to  jrive  separate 
si-nsations.  If  the  im|)ressions  follow  at  a  more  rapid  rate,  they 
will  he  fused  together  into  a  continuous  sensation. 

Touch-sensations  are  localized — i.  c,  they  are  referred  to  the 
right  portion  of  the  body  where  the  stimulus  is  applied.  This 
power  is  acquired  early  in  life  and  the  sensations  of  touch  are 
correlated  with  those  of  sight  and  those  arising  from  muscles,  so 
that  each  area  of  the  skin  acquires  a  ''local  xif/n."  The  power 
and  iineness  of  l()calizatit)n  ditler  greatlv  for  diti'erent  portions  of 
the  skin.      The  following  table  is  taken  from  Kirke's  ILnidbook : 

Table  op  Variations  in  the  Tactile  Sensibility  of  the 
Different  Parts.^ 

Tip  of  toiiprue 2?  iiit'li- 

I':iliii;u'  surface  of  third  pli;danx  of  forefinger j.j  " 

Tahnar  siu-face  of  sconiul  phalanges  of  fingers |  " 

lieil  snrfaoe  of  iimlci-  lip i  " 

Ti|)  of  tlie  nose i  " 

Middle  of  dorsnrn  of  tmiufue \  " 

Palm  of  hand ^j  " 

Centre  of  hard  palate ^  " 

Dorsal  snrfaee  of  lir.st  phalanges  of  finders l^z  " 

Back  of  hand \ H  " 

Dorsum  of  foot  near  toes Ij  " 

Glnteal  region H  " 

Sacral  region H  " 

Upper  and  lower  parts  of  forearm      li  " 

Back  of  ncek  near  oeeipnt 2  " 

Upper  dorsal  and  mid  lumbar  regions 2  " 

Mid<lle  part  of  fore;irtn •  2i  " 

Middle  of  thigh 2\  " 

Mid-eervieal  region 2i-  " 

Mid-dorsal  region      2l  " 

Tactile  areai^  liari\  in  i/cHrruK  an  oral  form  ivith  tlf  lomj  axix 
parallel  to  the   lomj   axin  of  the  jtortion  of  the  body  investigated. 

'  The  measurement  indicates  the  least  distance  at  which  the  two  blunted 
points  of  a  pair  of  compasses  could  be  separately  distinguished. —  K.  II.  Webec. 

\h — Phys. 


226  THE  SPECIAL  SENSES. 

These  areas  are  not  indicative  of  the  distribution  of  certain  nerves. 
The  important  factor  in  the  separation  of  two  points  that  are 
stimulated  is  not  that  two  different  nerves  shall  be  stimulated, 
but  that  there  must  be  a  certain  number  of  unstimulated  points 
between  those  stimulated. 

The  sense  of  touch  cau  be  greatly  educated  and  specialized. 
The  reading  of  raised  letters  by  the  blind  is  an  example.  Im- 
proved touch-discrimination,  attained  by  practice  upon  the  skin 
of  one  arm,  is  accompanied  by  an  improvement  in  the  correspond- 
ing area  of  the  other  arm,  but  not  of  any  other  areas  of  the  body. 
This  shows  that  the  localizing  power  \\qs>  within  the  central  system. 

The  skin  is  an  organ  for  the  detection  of  temperature-changes, 
and  its  power  in  this  respect  varies  in  different  portions  of  the 
body.  The  intensity  of  the  sensation  depends  upon  the  area  stimu- 
lated. There  is  very  little  doubt  that  there  are  two  distinct  tem- 
perature-nerves, which  serve,  respectively,  for  the  appreciation  of 
heat  and  cold.  The  areas  to  which  the  nerves  are  distributed  can 
be  located  in  the  skin  as  cold  and  heat  points.  That  this  sensa- 
tion is  distinct  from  ordinary  tactile  sensation  has  been  inferred 
from  the  fact  that  when  the  ordinary  touch  is  blunted  the  tempera- 
ture-sense remains  unimpaired.  Temperature-sensations  are  not 
accurate ;  they  are  only  relative — that  is,  the  temperature  of 
various  things  is  inferred  from  the  temperature  of  the  skin  and  its 
habitual  surroundings.  It  is  related  that  Arctic  explorers  have 
found  the  water  warm  when  swimming  in  pools  on  icebergs,  and  a 
drop  of  mercury  at  80°  F.  is  said  to  feel  cold  in  the  tropics.  A 
more  simple  illustration  is  that  of  immersing  one  hand  in  water  at 
40^  F.  and  the  other  in  water  at  120°  F.,  and  then  plunging  both 
into  water  at  80°  F.,  when  one  hand  will  feel  hot  and  the  other 
cold.  During  a  chill  the  temperature  of  the  body  is  often  very 
high,  and  yet  the  sensation  is  that  of  cold. 

COMMON  SENSATION. 

By  common  sensation  is  meant  that  state  of  mind,  more  or  less 
definite,  by  which  the  condition  and  position  of  the  body  at  any 
moment  are  known.  Such  perceptions  cannot  be  located  distinctly 
in  any  organ  or  set  of  organs,  as,  for  instance,  hunger,  thirst,  etc. 
Besides  these  there  are  some  sensations  which  involve  certain 
organs  which  must  be  classed  under  this  head  ;  thus  inclinations 


QUESTIOyS  ON  CHAPTER  XIII.  'I'll 

to  cough  or  to  sneeze,  to  vomit,  (lefecate,  und  urinate.  Many  of 
these  sensations  occupy  the  border-line  hetween  common  sensi- 
bility and  the  special  sense  of  touch,  such  as  tickling  and  itching. 
Pain  is  a  common  sensation,  but  is  allied  very  closely  to  touch. 
It  is  the  sensation  which  results  from  intensifying  any  common 
sensation,  and  ditlers  from  the  special  sensations  in  not  being  well 
localized  and  in  the  long  latent  period  that  precedes  its  develof)- 
ment.  According  to  one  investigator,  j)ain-point.s  are  se|)arate 
from  pressure-points  and  are  more  numerous.  More  than  lOU  are 
found  to  every  square  centimeter  of  the  skin,  and  they  require  1000 
times  as  great  a  stimulus  for  their  excitation  as  do  the  pressure- 
points. 

Hunger  and  thirst  are  })eculiar  sensations,  which  ordinarily 
depend  partly  on  local  and  partly  on  general  causes.  Local 
causes  of  hunger  and  thirst  are  an  empty  stomach  and  certain 
conditions  of  the  mucous  meni])rane.  These  sensations  are  felt 
largely  as  the  result  of  habit,  and  depend  thus  upon  the  condition 
of  secreting  and  absorbing  mechanisms. 

By  taking  a  body  in  the  hand  and  raising  it,  a  sense  of  resist- 
ance is  felt  in  the  muscles,  by  the  intensity  of  which  the  weight 
of  the  l)ody  can  be  determined  more  accurately  than  by  the  press- 
ure-sense alone.  This  is  called  the  muscular  soise.  It  is  devel- 
oped to  an  exceedingly  fine  degree  in  some  occupations  ;  for  ex- 
ample, postal  clerks  detect  overweight  letters  with  wonderful 
accuracy  and  quickness.  ]\Iuscular  sensation  is  allied  closely  to 
common  sensation.  It  may  be  due  to  a  consciousness  of  the 
amount  of  energy  sent  to  motor  cells  or  to  the  inflow  of  sensory 
impulses  which  indicate  the  tension  to  which  the  muscle  has  been 
subjected.  The  latter  view  is  corroborated  by  the  existence  of 
sensory  endings,  the  muscle-spindles,  in  muscles  and  tendons. 
The  centre  for  the  muscular  sense  is  in  the  upper  part  of  the 
quadrate  lobule  on  the  mesial  surface  of  the  heniisi)here.  Its 
involvement  by  pressure  lirings  al)out  inability  to  locate  the  posi- 
tion, say,  of  the  hand  or  foot  without  the  aid  of  sight. 

QUESTIONS  ON  CHAPTER  XIII. 

What  are  the  functions  of  the  eye  V 

Give  the  essential  parts  of  the  eye. 

What  are  primary,  sccojulary,  and  tertiary  positions  of  the  eye? 

How  is  an  image  formed  on  the  retina? 

Discuss  accommodation. 


228  THE  SPECIAL  SENSES. 

Discuss  the  effect  of  drugs  on  accommodation. 

Give  the  nervous  mechanisms  of  accommodations. 

Define  near-  and  far-points  and  the  range  of  accommodation. 

What  is  an  emmetropic  ej^e  ? 

Discuss  myopia  and  hypermetropia. 

What  are  presbyopia  and  astigmatism  ? 

Discuss  diplopia  of  the  eye. 

Define  spherical  aberration  and  achromatism. 

Give  the  nervous  mechanisms  that  control  the  iris. 

Discuss  intraocular  images. 

Why  does  the  pupil  appear  black  ? 

What  is  an  ophthalmoscope  ? 

What  are  the  most  important  structures  of  the  retina  ? 

What  are  the  blind  spot,  macula  lutea,  and  fovea  centralis  ? 

How  may  the  blind  spot  be  demonstrated  ? 

What  is  the  visual  purple  ? 

How  may  an  optogram  be  obtained  ? 

What  supplies  the  normal  stimulus  to  the  retina? 

Give  the  course  of  the  optic  fibres. 

What  constitutes  the  primary  vision  centre? 

Upon  what  physical  conditions  does  the  sensation  of  light  depend  ? 

How  can  it  be  shown  that  luminosity  is  recognized  more  easily  by  the  eye 
than  color  ? 

How  do  different  portions  of  the  retina  vary  in  their  power  to  distinguish 
color  ? 

Give  the  various  phases  of  the  activity  of  the  retina  when  stimulated. 

Distinguish  between  positive  and  negative  after-images. 

What  is  irradiation  ? 

What  is  the  relation  of  color  to  white  light? 

Discuss  the  color  theories. 

How  is  color-blindness  explained? 

What  is  the  proportion  of  color-blind  in  men  and  women?  What  reason 
can  be  given  for  this? 

Discuss  the  perception  of  distance. 

Discuss  the  illusion  produced  by  Zollner's  lines. 

Discuss  binocular  vision. 

Discuss  the  correction  for  the  inversion  of  the  retinal  image. 

What  does  clearness  of  vision  depend  upon? 

Where  are  the  physical  vibrations  of  sound  transformed  into  nervous  im- 
pulses ? 

How  do  the  sound-waves  of  the  air  reach  the  organ  of  Corti? 

Are  the  organs  of  Corti  absolutely  essential  to  the  appreciation  of  musical 
tones  ? 

How  are  the  impulses  conveyed  from  the  ear  to  the  brain  ? 

What  is  subjective  hearing  and  its  causes? 

Upon  what  factors  do  musical  sounds  depend? 

How  do  noises  differ  from  musical  sounds? 

What  is  the  musical  range  of  the  ear? 

What  is  the  range  of  audibility  of  the  ear? 

How  is  the  distance  of  sounds  estimated? 

Discuss  the  power  of  the  ear  to  appreciate  small  intervals  of  time. 

What  is  meant  by  equilibrium  of  the  body? 

How  is  the  sense  of  equilibrium  brought  about? 

What  is  the  effect  of  injury  to  the  semicircular  canals  of  an  animal? 


ni.rnonucTioN.  229 

What  proi.f  is  tlicrc  lliai  llir  sciiiiciiculiir  .aiials  aiil  in  pii-scrviiiK  iMjiiilil)- 

rium  ? 

What  is  llif  situatiuii  of  tlic  Dllacloiy  iiiiicdiis  nicmhraiu;? 

Wlial  is  llio  rdiulitidii  of  siiltstain-cs  tlial  cxcitf  siiicil  ? 

Wliat  is  tiu'  iminprtaiuc  (if  siiifll  in  llic-  lnwcr  animals V 

(!ivf  instaiu-is  of  tlic  dclicai-y  of  IIil-  imwvr  nf  smell  Y 

(iivc  tin-  ciiiir.-f  of  l\\v  (iH'aclory  lilni'S. 

I)is<-uss  till!  relation  of  common  siMisihility  and  .smell. 

What  is  the  location  of  the  .scnse-orKiUis  of  taste? 

What  are  the  nerves  of  t.isteY 

What  is  the  relation  of  smell  to  taste? 

Does  taste  (lei>eii(l  npon  concentration  (U- on  the  qnantity  of  the  stimulating 
.substance? 

How  is  taste  divided  ? 

Give  evidence  of  special  end-organs  for  each  divi.sion. 

How  does  cocaine  affect  the  seiisihility  of  the  tongue? 

What  is  the  function  of  the  ton},'iK!? 

What  is  an  after-taste? 

What  are  the  orj^ans  of  cutaneous  sensation? 

What  sensations  are  included  in  cutaneous  sensations? 

(live  Weber's  and  Feehner's  laws. 

Discuss  the  discriminating  power  of  diflerent  i)arts  of  the  body  to  pres.snre. 

What  interval  must  elapse  between  touch-stimuli  in  order  that  they  may 
give  .separate  impressions? 

DiseiLss  the  localization  of  touch-sensations. 

What  factor  determines  the  recognition  of  two  points  of  the  .skin  .stimuhited 
simultaneously? 

Discuss  the  situation  of  touch-areas. 

What  fact  shows  that  improved  touch-discrimination  is  a  central  phenom- 
enon ? 

Discuss  t em i)t-ra lure-sensations. 

What  is  a  common  sensation? 

Discuss  the  sensations  of  htinsrcr  ami  thirst. 

What  sensations  are  on  the  border-line  between  common  sensation  and 
special  sensation? 

What  evidence  is  there  for  separate  jiain-iioiiits  in  the  skin? 

What  is  meant  by  the  muscular  sense? 

Wliat  is  muscular  sense  due  to?    Locate  centre  and  give  effects  of  injury. 


CHAPTER    XIV. 

REPRODITCTTON. 

Reproduotiox  is  a  process  by  means  of  whicli  life  is  perpetu- 
ated because  tbe  existence  of  individuals  is  limited.  There  are 
tiro  mcfhrxJx  of  reiirodiiction — the  axexiinJ  and  the  sexual.  The 
former  is  the  more  jirimitive  form,  and  is  rostrictcil  to  the  lower 
oriranisms.      It  is  not  diHicidt  to  conceive  a  reason  for  reproduction 


230  REPRODUCTION. 

in  cells,  for  as  the  mass  of  living  matter  increases,  its  volume  in- 
creases as  the  cube,  while  its  surface  increases  only  as  the  square. 
There  will  finally  result  therefore  a  condition  when  the  absorptive 
surface  is  too  small  for  the  amount  of  living  matter,  and  a  division 
will  cause  a  relative  increase  of  surface.  Sexual  reproduction  is 
derived  probably  from  the  asexual  method,  and  consists  in  the 
union  of  male  and  female  elements.  The  most  primitive  examples 
are  to  be  found  in  some  of  the  unicellular  organisms  where  there 
is  a  fusion  of  the  two  sexes,  known  as  conjugation.  The  resultant 
mass  divides  and  so  produces  its  offspring.  In  somewhat  more 
highly  differentiated  forms  there  are  simply  an  exchange  and  a 
fusion  of  nuclear  matter.  In  the  higher  animals  there  is  a  fusion 
of  nuclear  matter  of  two  individuals  brought  about  by  the  produc- 
tion of  two  kinds  of  sexual  cells — ova  and  spermatozoa.  In  some 
animals,  like  the  worms,  both  sexual  elements  exist  in  the  same  in- 
dividual, but  this  condition  is  found  only  abnormally  in  the  highest 
animals.  Here  the  sexes  present  wide  anatomical,  physiological, 
and  psychological  differences.  These  differences  fall  into  two 
groups — jjrimary  and  secondary.  The  primary  sexual  characters 
are  the  most  pronounced,  and  consist  of  those  pertaining  to  the 
sexual  organs  and  their  functions.  The  secondary  sexual  charac- 
ters are  accessory  to  the  primary  ones,  and  include  the  differences 
in  voice,  growth  of  hair  on  the  face,  the  mammary  glands,  etc.,  in 
man  and  woman. 

The  sexual  cells  differ  widely  in  appearance.  The  spermatozoon 
consists  of  an  elliptical  head,  a  short  middle  piece,  and  a  tapering 
tail.  It  is  undoubtedly  a  cell  which  arises  from  a  testicular  cell 
known  as  the  spermatocyte.  The  latter  divides  into  four  spermatids 
which  grow  directly  into  spermatozoa.  It  is  important  as  well  as 
interesting  to  know  that  the  number  of  chromosomes  in  the  head 
of  the  spermatozoon  are  one-half  the  number  normally  present  in 
the  body-cells  of  the  individual.  The  spermatozoon  is  adapted  to 
vigorous  activity.  It  seeks  the  ovum  by  means  of  the  movements 
of  its  tail,  which  is  lashed  from  side  to  side,  causing  it  to  progress. 
and  at  the  same  time  to  rotate.  The  rapidity  with  which  it  moves 
is  from  1.2  to  3.6  mm.  per  second.  Spermatozoa  will  live  in  the 
male  genital  passages  for  months,  and  they  probably  will  live  in 
the  female  for  a  long  while,  but  the  exact  time  is  not  known.  They 
are  produced  in  large  numbers.  One  estimate  puts  the  production 
at  226,257,000  per  week.     The  spermatozoa  are  contained  in  a 


iiu'i-jihrrrios.  231 

Hnid  which  conies  from  tlie  ivMrx  partly,  luil  chiefly  from  acceHaunj 
.scrua/  (j/tiiiilx — the  siiuiiKtl  rcKiclrx,  [\\v  jnostnfr  ij/mid,  ami  (  oirjjcr  » 
glands.  Together  these  coiistitiu'iits  form  the  xvmni,  which  may 
be  described  as  a  vvliiiish  viscid  fluid  with  ii  characteristic  odor. 
The  amount  passed  at  a  time  is  from  O.o  to  6  c.c.  In  some  ani- 
mals it  contains  fihriiKxjcn,  which  enal)les  it  to  clot  within  the 
female  passages,  thus  preventing  esca|)e  of  the  spermatozoa. 

The  arum  in  its  j)erf'ected  state  as  it  leaves  the  (Irudfuni  J'ol/ir/r 
is  founil  to  be  a  minute  globular  cell  containing  a  nucleus  and 
nucleolus  as  well  as  a  cell-membrane.  It  undergoes  a  process 
analogous  to  what  takes  place  in  the  formation  of  a  spermatozoon, 
which  is  known  as  maturation.  It  begins  as  the  ovum  is  leaving 
the  ovary,  anil  consists  of  a  karyoJdvetlc  division  of  the  nucleus 
twice  in  succession.  With  each  division  half  of  the  nucleus  is 
extruded  together  with  a  small  amount  of  protoplasm  as  the  jtolar 
bodies.  The  first  i)olar  body  usually  divides  into  two  parts,  mak- 
ing three  jKilar  bodies,  all  of  which  degenerate.  As  the  result  of 
these  divisions  the  ovum  has  left  one-half  of  the  nnndier  of  chro- 
mosomes of  a  body-cell.  The  union  of  the  nuclei  of  ovum  and 
spermatozo<")n  restores  to  their  original  nund)er  the  chromosomes  of 
the  species.  Ova  are  develoi)ed  within  specialized  cavities  of  the 
ovarv  lined  bv  epithelial  cells  known  as  Graafian  follicles.  A 
Graafian  follicle  moves  toward  the  surface  of  the  ovary,  ruptures, 
and  discharges  the  ovum,  giving  rise  to  the  process  of  ovulation. 
This  is  in  most  animals  a  periodic  phenomenon,  and  in  woman 
probably  begins  at  puberty  with  the  first  menstruation  and  con- 
tinues until  the  climacteric.  Gases  of  pregnancy  at  the  ages  of 
seven,  eight,  and  nine  years  show  that  it  may  occur  very  early. 
After  the  ovum  has  been  set  free  from  the  ovary  it  in  some  unknown 
manner  reaches  the  Fallopian  tubes.  It  is  possible  that  in 
woman,  as  has  been  observed  in  some  animals,  the  fimbriated  ends 
of  the  tubes  clasp  the  ovaries  when  the  eggs  are  discharged.  The 
cilia  lining  the  tubes  gradually  carry  the  Q^\i:  toward  the  uterus, 
which   it  reaches  in  from  four  to  eight  days. 

Imprequiition  or  fertilization  usually  takes  place  in  the  tubes 
because  the  cilia,  while  they  carry  the  ovum  in  one  direction,  act 
as  a  guiding  stimulus  to  the  spermatozoa,  whi<'h  move  in  the  oppo- 
site (lirection  to  meet  the  ovum.  In  case  the  ovum  is  fertilized,  it 
passes  on  to  the  uterus,  where  it  is  retained  and  develops  to  the 
end  of  the  endjryonic  period. 


232  REPR  OD  UCTION. 

The  uterus  is  active  monthly  iu  that  it  discharges  a  bloody, 
mucous  liquid  through  the  vagina.  This  is  called  menstruation. 
Some  days  before  the  flow  the  mucous  membrane  of  the  body  of 
the  uterus  begins  to  thicken  by  the  growth  of  its  connective  tissue 
and  by  the  engorgement  of  its  bloodvessels  until  it  is  from  two  to  three 
times  its  normal  thickness.  The  swollen  capillaries  become  rupt- 
ured and  the  epithelial  cells  undergo  a  fatty  degeneration.  Usually 
only  the  superficial  portions  of  the  mucous  membrane  are  involved, 
and  those  cases  where  it  is  removed  to  its  deepest  layers  are  very 
likely  pathological.  The  flow  continues  for  four  days  or  more, 
during  which  100  to  200  c.c.  of  blood  are  lost.  The  latter  is 
slimy  with  mucus,  does  not  coagulate,  contains  disintegrated  tis- 
sue, epithelial  cells,  and  has  a  characteristic  odor.  Menstruation 
is  accompanied  by  many  other  symptoms.  The  ovaries  and  breasts 
are  congested,  dark  rings  form  about  the  eyes,  mental  depression 
often  exists,  skin  and  breath  have  a  characteristic  odor.  The  in- 
termenstrual period  exhibits  a  gradual  increase  in  nervous  tension 
and  metabolic  activity,  manifested  in  an  increased  production  and 
excretion  of  urea,  in  a  higher  temperature,  and  an  increase  in  the 
strength  and  rate  of  the  heart-beat.  These  reach  their  maximum 
a  few  days  before  the  menstrual  flow,  and  then  undergo  a  rapid 
fall,  reaching  a  minimum  with  the  cessation  of  the  flow.  The 
first  menstruation  is  an  index  of  puberty,  and  occurs  in  temperate 
climates  at  the  age  of  from  fourteen  to  seventeen.  The  time  varies 
with  the  climate,  food,  growth,  environment,  etc.  Occasionally 
menstruation  may  be  entirely  absent  in  otherwise  normal  women. 
The  removal  of  the  ovaries  puts  an  end  to  further  menstruation. 
Its  cessation  at  the  age  of  forty-five  to  forty-eight  marks  the  meiv- 
opause  or  climacterie. 

The  meaning  of  menstruation  has  been  much  discussed.  In  the 
lower  mammalia  reproduction  is  limited  to  seasonal  periods,  which 
are  characterized  by  sexual  excitement,  congestion  and  swelling 
of  the  external  genital  organs,  and  a  uterine  discharge.  During 
the  remainder  of  the  year  sexual  excitement  is  absent.  These 
periods  of  excitement  are  known  as  rut  or  heat.  Domestication 
with  its  regular  food-supply  and  care  has  increased  productiveness 
by  rendering  the  reproductive  periods  more  frequent.  This  has 
taken  place  iu  like  manner  in  the  human,  but  has  progressed 
further  in  that  woman  during  the  menstrual  flow  has  largely  lost 
sexual  desire.     According  to  Pfliiger,  menstruation  is  a  prepara- 


iiKi'iinnrcTioy.  2.'i3 

tion  of  the  uterine  surface  for  the  reception  of  the  inipre;^nated 
egg.  The  nwclitniixui  hy  which  the  uterus  is  prepared  is  aa 
follows — 

The  growth  of  tlie  cells  of  the  ovary  reflex ly,  l>y  constant 
stiuiulalion  of  the  spinal  cord,  causes  a  dilatation  of  the  vessels  of 
the  genital  organs,  which  results  in  a  breaking  down  of  the 
mucous  nuMuhrane  of  the  uterus.  At  the  same  time  the  increased 
hlood-supply  causes  a  ripening  of  the  (Jraaiian  iollicle.  It  is  the 
general  view  that  ovulation  and  menstruation  are  the  result  of  a 
conuuou  cause,  but  either,  in  the  human,  may  occur  without  the 
other.  It  is  probable  that  ovulation  takes  place  a  few  days  before 
the  onset  of  the  menstrual  period. 

('aj>n!(tti()ii  is  the  act  of  sexual  union  th:vt  has  for  its  object  the 
introduction  of  semen  into  the  genital  passages  of  the  female.  It 
is  preceded  by  a  preliminary  period  of  sexual  excitement,  during 
which  the  i)enis  becomes  swollen,  turgid,  and  erect,  while  the 
vulva  also  becomes  firm  and  turgid.  There  are  vaf^rahir  phenomena. 
In  the  penis  the  arteries  relax,  tilling  the  cavernous  spaces  with 
blood,  while  simultaneously  the  exit  of  the  blood  is  prevented  by 
the  contractions  of  the  erector  penis  and  bulbocarernosKs  muscles. 
The  penis  is  then  introduced  into  the  vagina,  and  as  a  result  of 
muscular  movements  producing  friction  U])on  delicate  sensory 
nerve-endiugs  of  the  glans  penis  and  clitoris  there  are  produced 
intense  nervous  sensations  which  lead  to  a  cUnia.r  or  orr/a.wi,  con- 
sisting of  the  ejnnihdion  of  the  semi)ial  tluid  into  the  upper  end 
of  the  vagina.  There  is  at  the  same  time  a  secretion  in  the 
female  from  the  r/fanrls  of  Bartholin,  and  perhaps  also  rhythmical 
opening  and  ckmnff  of  the  cervical  canal.  Erection  is  a  reflex  act, 
the  centre  Iving  in  the  lumbar  cord.  It  may  be  aroused  by  im- 
pulses arising  from  the  walls  of  the  testes  due  to  the  pressure  of 
contained  semen,  or  from  the  nerve-endings  in  the  skin  of  the 
penis  or  from  the  brain.  The  efferent  nerves  are  the  yiervi  eri- 
genie!^.     The  clitoris  is  the  homologue  of  the  penis. 

The  sexual  excitement  accompanying  an  orgasm  is  more  intense 
usually  in  the  male.  The  diHrhnrr/e  of  semen  begins  with  power- 
ful peristaltic  waves,  probably  in  the  rasa  efferentia,  and  ends  with 
rhi/thmic  contractions  of  the  ischiocavernosns  and  bttlbocaveniosns 
muscles.  This  is  also  a  rellex  act  with  the  centre  in  the  hnnbar 
portion  of  the  cord.  The  spermatozoa  ))robably  reach  the  Fallo- 
pian tube   mainly  by  their  own   movements,  but  it  is  possil)le  that 


234  BEPR  OD  UCTION. 

after  coitus  the  uterus  may  exert  a  suction  and  draw  them  from 
the  vagina.  It  is  claimed  by  some  that  the  uterus  dips  down  into 
the  pool"  formed  by  the  discharged  semen.  The  time  involved  in 
the  passage  of  the  spermatozoa  to  the  ovary  is  unknown,  except 
that  it  is  quite  short ;  in  the  rabbit  the  time  is  only  two  and  three- 
quarters  hours.  When  spermatozoa  meet  an  ovum,  they  surround 
it  in  great  numbers  until  one  of  them  succeeds  in  uniting  with 
the  Qgg,  after  which  the  remainder  perish.  When  fertilized,  the 
ovum  undergoes  repeated  segmentation,  increases  in  bulk,  histolog- 
ical differentiation  and  the  physiological  division  of  labor  set  in, 
until  finally  there  results  a  new  individual  that  is  expelled  at 
the  proper  time.  In  stick  cases  where  more  than  one  spermato- 
zoon succeeds  in  entering  the  ovum  (^polyspermy)  the  embryo  dies 
early. 

While  in  the  uterus  the  growing  foetus  derives  by  far  the 
greater  part  of  its  nourishment  from  the  mother  by  means  of  the 
placenta.  Here  the  circulation  of  the  child  is  brought  into  intimate 
relation  to  that  of  the  mother,  but  they  are  nevertheless  separated  by 
four  layers  of  cells  : 

1.  The  wall  of  the  choriouic  capillary. 

2.  The  cells  of  the  chorion. 

3.  The  cells  of  the  uterine  follicle. 

4.  The  wall  of  the  uterine  sinus. 

Although  there  is  no  direct  communication,  there  is  an  exchange 
of  material  between  the  mother's  blood  and  the  foetal  blood.  The 
mother's  blood  furnishes  to  the  foetal  blood  food  and  oxygen,  and 
in  turn  removes  the  carbon  dioxid  and  excrementitious  material 
which  the  foetus  must  lose.  The  placental  circulation  supplies  the 
place  taken  in  after-life  by  the  alimentary  and  respiratory  tracts. 
When  the  placenta  is  expelled,  a  part  of  the  maternal  tissue  is 
left  behind,  and  there  is,  of  course,  a  loss  of  blood  contained  in 
the  uterine  sinuses,  but  the  general  balance  of  the  circulation  is 
not  disturbed  at  childbirth.  The  reason  for  this  is  the  oblique 
entrance  of  the  placental  vessels.  They  enter  the  sinuses  at  an 
angle,  and  are  therefore  compressed  by  the  muscular  tissue  of  the 
uterus  in  its  contracted  state.  There  are  two  distinct  types  of 
circulation  in  foetal  life — the  vitelline  and  the  placental  circulation. 
In  both  types  the  blood  is  driven  on  by  the  heart,  the  essential 
difference  being  the  site  where  the  foetal  blood  is  enriched.  The 
vitelline  circulation  precedes  that  of  the  placenta,  and  as  soon  as 


RF.vuoi)  I V  'Tio.v.  2:35 

tlie  latter  is  formed  the  ionuer  disappears.      Tlie  vitiHiiie  ciicula- 
tiou  ill  the  liiniian  is  very  short-lived. 

Thii  placental  circitlatiuii    presents   two    proininent    lealiires    in 
which  it  dif}ei*s  from  a<lult  cireulation — 

1.  IModiiications  are  necessary  in  the  heart  and  i^rcat  lilootlvcs- 
sels  in  order  that  the  hh)od  may  enter  the  Inngs. 

2.  In  the  circulation   through  the  liver  the  veins  are  nKidified 
so  as  to  allow  i'or  the  return  of  placental  circulation. 

The  course  of  the  f(dal  circulation  is  as  follows:  The  f«elal 
blood,  puriiied  and  enriched  in  the  placenta,  passes  hy  the  um- 
bilical vein  in  the  und)ilical  cord  to  the  under  surface  of  the 
liver  ;  here  the  vein  divides  into  two  parts.  One  portion  of  the 
blood  enters  the  liver  substance,  and  after  traversing  its  capillaries 
is  pouretl  out  by  the  hepatic  veins  into  the  inferior  vena  cava. 
The  other  portion  of  the  blood  passes  directly  from  the  und)ilical 
vein  to  the  inferior  vena  cava  by  means  of  a  blood-channel,  the 
ductus  venosus.  The  blood  of  the  vena  cava  inferior  is  carried  to 
the  right  auricle  of  the  heart,  and  instead  of  passing  from  there  into 
the  right  ventricle,  as  iu  the  case  of  the  adult  heart,  it  goes  di- 
rectly into  the  left  auricle  by  means  of  an  opening  iu  the  auricu- 
lar septum,  known  as  the  foramen  ovale.  The  flow  of  blood  from 
the  inferior  vena  cava  through  the  foramen  ovale  and  into  the 
left  auricle  is  facilitated  by  the  fact  that  the  inferior  vena 
cava  points  almost  tlirectly  into  the  foramen  ovale.  The  Eusta- 
chian valve,  consisting  of  a  crescentic  fold  of  fibrous  tissue  cov- 
ered with  endocardium  and  extending  from  a  point  between  the 
opening  of  the  sujierior  and  inferior  venre  cavjxi  over  to  the  lower 
and  anterior  margin  of  the  foramen  ovale,  also  favora  this  pecu- 
liar course  of  the  blood.  The  base  of  the  fold  lies  on  the  right 
auriculoventricular  ring,  and  the  concavity  of  the  fold  is  directed 
upward.  From  its  position  the  Eustachian  valve  acts  as  a  guid- 
ing groove  or  gutter  for  passing  the  blood  from  the  inferior  vena 
cava  to  the  foramen  ovale.  On  entering  the  left  auricle  the  blood 
is  i)assed  into  the  left  ventricle  and  thence  into  the  aorta,  to 
be  distributed  all  over  the  body  ;  but  principally  to  the  head 
and  upper  extremities.  From  the  latter  regions  the  blood  re- 
turns to  the  heart  by  the  superior  vena  cava.  On  entering 
the  right  auricle  the  blood  from  the  superior  vena  cava  pas.«es 
in  front  of  the  stream  that  Hows  from  the  inferior  vena  cava 
to  the  foramen  ovale,  and  enters  the  right  ventricle.     The  direction 


236  REPR  0  D  UCTION. 

in  which  the  superior  vena  cava  points  (toward  the  auriculo- 
ventricular  ring),  and  also  the  Eustachian  valve,  are  the  factors 
that  determine  the  separation  of  the  two  streams.  On  enter- 
ing the  right  ventricle  the  blood  from  the  superior  vena  cava 
is  forced  into  the  pulmonary  artery  toward  the  lungs.  Before 
reaching  the  lungs  this  blood  meets  with  a  channel  of  communi- 
cation between  the  pulmonary  artery  and  the  aorta-(ductus  arteri- 
osus), into  which  the  larger  portion  of  the  blood  from  the  pul- 
monary artery  enters  and  mingles  with  the  blood  of  the  aorta ; 
the  remainder  passes  along  the  pulmonary  artery  to  the  structure 
of  the  lungs,  which  it  nourishes,  and  thence  back  to  the  left  auri- 
cle by  means  of  the  pulmonary  veins. 

The  blood  iu  the  aorta  that  comes  from  the  left  ventricle  passes 
largely  to  the  head,  but  that  which  enters  from  the  ductus  arteri- 
osus largely  passes  into  the  descending  aorta.  On  passing  down 
the  descending  aorta,  some  of  the  blood  enters  the  mesenteric 
arteries,  and  thence  back  to  the  venous  circulation  by  means  of 
the  portal  vein  and  the  liver.  Some  of  the  blood  enters  the  iliac 
arteries  and  nourishes  the  lower  extremities  ;  but  the  major  part 
of  the  blood  leaves  the  foetal  body  by  the  hypogastric  arteries. 
The  hypogastric  arteries  are  branches  of  the  internal  iliacs,  and 
course  along  the  abdomen  to  leave  the  foetal  body  at  the  umbili- 
cus, where  on  emerging  they  change  their  names  to  umbilical 
arteries  and  proceed  to  the  placenta. 

The  liver,  receiving  the  freshest  blood  (from  the  umbilical  vein), 
is  the  best  nourished  of  all  the  organs  of  the  foetus.  The  result 
is  that  the  foetal  liver  is  vastly  larger  in  proportion  than  the  adult 
liver.  The  branches  of  the  aorta  given  off  to  the  head  and  upper 
extremities  distribute  blood  from  the  inferior  vena  cava,  while 
the  ductus  arteriosus,  carrying  the  blood  from  the  superior  cava 
and  right  ventricle,  enters  the  aorta  in  such  a  way  that  most  of 
its  blood  is  sent  to  the  lower  extremities,  abdominal  organs,  and 
umbilical  arteries.  In  this  way  the  deoxidized  blood  is  sent  back 
to  the  placenta  for  the  renewal  of  its  oxygen.  The  lower  ex- 
tremities are  less  developed  than  the  upper.  There  are  two  rea- 
sons for  this  : 

1.  The  blood  contains  less  oxygen  and  nourishment. 

2.  The  internal  iliac  arteries,  giving  off  the  umbilical  arteries, 
divert  a  considerable  portion  of  the  blood-supply  from  the  exter- 
nal iliacs  which  go  to  the  lower  extremities. 


iiFJ'iiohrcTioN.  237 

Owiiii,'  to  the  (liictiis  arteriosus,  hut  liltlc  blood  ^'ocs  to  tlu'  liiiifrs. 
Tlie  amount  is  sutlifienl,  however,  to  keep  up  the  nutrition  of  the 
lunjjs,  anil  they  liave  no  function  helbre  hirth. 

The  re-yiiratori/  ceiitir  in  the  niechilla,  whieli  lias  heen  <piie.seent 
because  it  has  been  well  supplied  with  oxygen,  is  awakened  as 
soon  as  the  eonneetion  with  the  uterine  sinuses  is  interrupted.  As 
soon  as  the  supply  of  oxygen  sinks  to  a  certain  point,  an  Imjmlne 
of  'niK}iir<iii(i)i  is  generated,  and  as  the  infant  breathes  the  lungs 
assume  a  comlition  of  partial  expansion.  With  the  diminished  re- 
sistance in  the  ex|)anded  lungs  the  amount  of  blood  in  the  ])ulmon- 
ary  circulation  increases,  and  as  the  amount  passing  through  the 
ductus  ar^enW^.s consequently  decreases,  this  soon  is  obliterated.  At 
the  same  time  the  amount  of  blood  returning  to  the  left  auricle  in- 
creases in  (juantity,  and  the  intra-auricular  pressure  becomes 
greater;  then,  too,  the  inferior  vena  cava  sends  less  blood,  for  the 
ductus  venosus  no  longer  carries  the  blood  from  the  placental  cir- 
culation, and  therefore  the  foramen  ovale  is  not  used,  and  is  soon 
closed  by  the  adhesion  of  its  valve-like  curtain.  Thus,  the  adult 
circulation  is  established  in  place  of  the  fcetal  circulation  in 
consequence  of  res))iratory  movements.  Owing  to  the  division 
and  occlusion  of  the  umbilical  cord,  blood  no  longer  passes 
through  the  umbilical  vessels,  with  the  result  that  the  um- 
bilical vein  degenerates  into  a  fibrous  cord  (round  ligament  of 
the  liver).  Tlie  hvpogastric  arteries  remain  pervious  for  the 
first  part  of  their  course,  as  the  sujjerior  vesicle  arteries;  but  the 
remainder  of  their  course  is  obliterated  and  degenerates  into  fibrous 
cords. 

The  period  of  gestation  during  which  the  embryo  is  developing 
in  the  uterus  may  be  put  at  2M0  days,  and  probably  dates  from 
the  finst  day  of  the  last  menstruation.  Owing  to  the  ditiiculty  of 
knowing  the  time  of  fertilization,  the  exact  period  is  not  known. 
One  of  the  earliest,  and  most  obvious  and  most  usual,  signs  of 
pregnancy  is  the  cessation  of  menstruation.  The  caii.^c  of  the 
expulsion  of  the  f<etus  from  the  uterus  is  not  well  known,  and  it 
is  probable  that  on  account  of  the  exceeilingly  irritable  condition 
of  the  uterus  a  number  of  causes  may  exist.  Among  these  have 
been  suggested  the  pressure  on  the  tissue  of  the  uterus  or  on  the 
ganglia  of  the  cervix,  and  the  gradually  increasinir  venosity  of 
the  f(X'tal  blood. 

The   frequency  of  mn/tiple  convejitions  is  for  twins  at  a  ratio  of 


238  REPRODUCTION. 

1  :  120  ;  for  triplets,  1  :  7910  ;  and  for  quadruplets,  1  :  371,126 
births.  Tivins  may  arise  from  separate  eggs  or  from  a  single  egg. 
The  presence  of  a  double  chorion  is  diagnostic  of  the  former,  and 
a  single  chorion  of  the  latter.  The  separate  ova  may  come  from 
a  single  Graafian  follicle  or  not.  When  the  offspring  come  from 
separate  ova,  they  may  be  of  separate  sexes,  and  do  not  neces- 
sarily resemble  one  another  ;  but  whenever  they  come  from  the 
same  ovum,  by  a  separation  of  the  blastomeres,  they  are  of  the 
same  sex,  and  their  personal  resemblance  is  very  great. 

The /actors  that  determine  sex  are  very  little  understood.  As  a 
general  rule,  more  boys  are  born  than  girls.  The  sexual  organs 
are  difiTerentiated  at  the  eighth  week  of  uterine  life,  but  it  is  im- 
possible to  say  whether  the  sex  is  determined  in  the  germ-cells,  in 
fertilization,  or  during  the  early  life  of  the  embryo.  Many  hy- 
potheses have  been  offered.  According  to  the  Hojacker- Sadler 
law,  if  the  father  is  older  than  the  mother,  more  boys  are  likely  to 
be  born  ;  but  if  the  mother  is  the  older,  the  probability  of  girls  is 
still  greater.  Breeders  have,  with  great  success,  made  use  of  the 
rule  that  the  earlier  the  ovum  is  fertilized  after  liberation  the 
greater  is  the  tendency  to  females  ;  the  later  the  fertilization  takes 
place,  the  greater  is  the  probability  of  males  resulting.  Schenk 
takes  a  similar  view  in  that  the  ovum  in  its  earlier  stages  is  con- 
sidered unripe.  The  presence  of  sugar  in  the  urine  of  a  pregnant 
woman  he  regards  as  an  indication  of  incomplete  metabolism  of 
the  body  which  results  in  a  tendency  to  females.  By  means  of  a 
highly  nitrogenous  diet  he  claims  to  make  the  metabolism  more 
perfect  and  insure  the  production  of  male  offspring.  The  sex  in 
some  of  the  lower  organisms  has  been  altered  at  will  by  feeding  and 
by  temperature.  Taking  all  the  ascertained  facts  into  consideration, 
it  seems  probable  that  whenever  the  parents,  especially  the  mother, 
are  surrounded  by  unfavorable  nutritive  conditions,  the  production 
of  males  will  result ;  while  favorable  nutritive  conditions  result  in 
females.  It  may,  moreover,  be  said  that  the  production  of  sex  is 
self-regulating,  inasmuch  that  a  scarcity  of  the  sex  of  one  kind 
tends  to  a  production  of  individuals  of  that  sex.  Another  theory 
states  that  whichever  parent  possesses  the  higher  sexual  energy  (not 
to  be  confounded  with  sexual  desire)  will  determine  the  sex  of  the 
offspring,  but  always  of  the  opposite  line — e.  g.,  females  of  higher 
energy  produce  males. 


Qi'i:sTroys  ox  ciiaptf.ii  xiv.  239 

Ql'KSTIONS  ON    CIlAI'Ti:!;    XIV. 

Wliat  is  rrprntliictiou  V 

How  many  iiu-tliodsaro  tlicrcV 

l)fscril>i'  the  asexual  iiii-thod. 

Wliy  (iiK's  a  ;ir()\viii;{  mass  of  iirotoiilasm  divide? 

What  is  tiif  cssi-ntial  Tact  of  sexual  reiiroiliu-lion'.' 

Deserilte  various  sta;,'es  in  the  develo|mieiit  of  sexual  reproducticii). 

What  are  the  primary  and  secondary  sexual  characters? 

Describe  the  development  of  a  si>ermato/,oon. 

What  diU'erence  is  tlu're  lulween  the  sexual  elements? 

lu  what  respects  are  they  alike? 

What  is  the  rale  of  movement  of  a  spermatozoon? 

What  is  semen? 

What  is  meant  hy  the  maturation  of  the  ovum? 

What  is  a  Ciraalian  follicle? 

Descrihe  ovulation. 

How  does  the  ovum  reach  the  uterus? 

What  is  fertiliwitiou  ?     Where  does  it  take  jdace? 

Describe  the  process  and  development  of  menstruation. 

How  long  does  menstruation  last  ?  What  are  the  symptoms  accompany- 
ing it? 

Give  the  physiological  causes  of  menstruation. 

Discuss  puberty. 

What  is  the  menojiause? 

What  is  the  object  of  menstruation? 

W'hat  is  the  relation  of  ovulation  to  menstruation? 

Describe  copulation. 

Discu.ss  the  erection  of  the  penis. 

Discuss  the  nervous  mechanism  of  an  orgasm. 

How  do  spermatozoa  reach  the  Fallopian  tubes? 

What  is  polyspermy  ? 

How  many  ty])es  of  foetal  circulation  are  there? 

Describe  the  placental  circulation. 

What  changes  take  jtlace  in  fietal  circulation  at  birth? 

What  is  the  length  of  the  period  of  gestation  in  the  human  being?  From 
what  time  does  it  jirobablj-  date? 

What  is  the  earliest  sign  of  pregnancy? 

What  is  the  cause  of  the  exjiulsion  of  the  foetus  from  the  uterus? 

Di.scu.ss  the  occurrence  f)f  twins. 

Discuss  the  determination  of  sex. 

What  is  the  Hofacker-Sadler  law? 

What  is  Schenk's  hypothesis? 

What  are  the  most  probable  determining  factors  of  sex? 

Is  the  production  of  sex  self-regulating? 


APPENDIX. 


CHEMICAL  TESTS  COMMONLY  USED  IN  PHYSIOLOGICAL  ANALYSIS. 

Fob  Proteids  : 

Nitric  Acid  coagulates  all  except  jjeptones. 

Heal. — All  are  coagulated  hy  boiling,  except  peptones. 

Xanthroprotrir  JiidfliDii. — A  solution  boiled  with  strong  nitric  acid  becomes 
yellow:  the  color  is  deepened  i)y  the  addition  of  aninjoiiia. 

Biuret  Rcdrtioii. — With  a  trace  of  copper  sulphate  and  an  excess  of  po- 
tassiinn  or  sodium  hydrate  tliey  give  a  purple  reaction. 

Millon's  licucliuii. — With  a  solution  of  metallic  mercury  in  strong  nitric 
acid  (Millons  reagent)  they  give  a  white  or  pinkish  reaction,  and  the  color 
becomes  more  pink  on  boiling. 

For  Starch : 

Iodine  Ecactioii. — Add  to  a  solution  of  starch  a  small  quantity  of  tincture 
of  iodine,  and  a  blue  reaction  results.  The  color  disappears  on  heating  and 
returns  on  cooling. 

(itycogen. — Same  test  gives  reddish  reaction,  port-wine  color,  which  dis- 
appears on  heating  ajid  returns  on  cooling. 

For  Sugar  (Gluco.'^e)  : 

Moore'?,  Test. — Boil  solution  of  sugar  with  an  excess  of  potassium  hydrate, 
brown  color-reaction. 

Trommer's  Test. — Add  to  solution  a  sufficient  amount  of  potassium  hydrate 
to  render  it  quite  strongly  alkaline.  Then  add  a  solution  of  copper  sulphate, 
drop  by  drop,  until  a  distinct  lilue  tinge  is  visible.  Heat,  and  the  presence 
of  sugar  is  shown  by  appearance  of  red,  yellow,  or  orange  color-reaction. 

Fehliiif/s  Tei(t  Solution.  —  An  alkaline  copper  solution  by  which  a  quantita- 
tive test  may  be  made.  The  solution  is  somewhat  unstable,  and  is  for  this 
reason  to  be  tested  by  boiling  before  using.  The  strength  of  the  solution  is 
such  that  1  cubic  cni.  (15  minims)  will  be  exactly  decolorized  by  7,-J(,  of  a 
gramme  (0.075  grain)  of  glucose.  This  test  is  very  delicate,  and  is  quite 
commonly  used  for  urinary  examinations  to  detect  glycosuria. 

The  Fermentation  Tesl.—ll'  a  small  (juantity  of  yeast  be  addeil  to  a  sugar 
solution,  the  fungus  of  the  yeast  (saccharomyces)  will  cause  the  sugar  to  be 
decomposed  into  carbonic  acid  and  alcohol,  if  the  process  be  continued 
until  tlie  sugar  is  entirely  broken  up,  the  amount  of  carbon  dioxide  evolved 
indicates  the  proportion  of  sugar  present. 

For  Bile  Salts: 

Pettenkofer's  Ti'."!. — Upon  the  addition  of  sulphuric  acid  to  a  .solution  of 
bile-sidts  in  water  there  is  a  precipitation  of  the  salts,  which  arc  redissolved 
by  a  further  addition  of  the  acid.  If  a  drop  of  a  solution  of  cane-sugar  be 
added,  a  deep  cherry  color  is  developed. 

16— Phys.  241 


242 


APPENDIX. 


For  Bile  Pigments  : 

Gmelin's  Te-4. — Add  a  small  quantity  of  nitroso-nitric  acid  to  a  solution 
of  the  bile  pigments,  and  a  play  of  colors  results,  besrinning  with  green  and 
changing  to  blue,  violet,  red,  ami  yellow.  Tliis  is  seen  best  on  a  white  back- 
ground; therefore  a  plate  is  often  used  for  this  test. 

METRIC    SYSTEM. 


1  Inch                            -2                                   '3                                 4 

1 

Millimetres. 

2            .3            .  -t               5               6            1  7            id            1  9     10 
Ceu.jnetres. 

The  area  of  the  figure  within  the  heavy  lines  is 

that  of  a  square  decimetre.     A  cube  one  of  whose 

sides  is  this   area   is   a  cubic   decimetre   or  litre.     A 

litre  of  water  at  the  temperature  of  4°  C.  weighs  a 

Jdlofframme. 

A  litre  is  1.76  pint ;  a  pint  is  0.568  of  a  litre. 

The  smaller  figures  in  dotted  lines  represent  the 

areas  of  a  square  centimetre  and  of  a  squre  inch. 

A  cubic  centimetre  of  water  at  4°  C.  weighs  a 

gramme. 

i 
i 

i         Sqaare  Inch. 

Sqnare  : 

Centi-   : 

me-.re. 

niPORTANT  EQUIVALENTS  OF  THE  METRIC  SYSTEM. 
Gramme         ^loi  grains.  Metre  =39|  inches. 


Centigramme  ^  /^  grain. 
Milligramme  =  j^,  grain. 
Kilogramme  ^=  2.2  pounds. 


Centimetre 
Millimetre 
Micromillimetre 


^1  inch. 

—  ^  inch. 

—  jrkins  inch 


COMPARATIVE   SCALES,  showing  at  a  glance  the  exact  e^iulvaJent  of 
ordinaxy  weights  and  measurea  in  those  of  the  Metric  Sj-stem.  and  vien  vena. 


CENTliSRAOe 


FAHRENHEIT 


OECISnAMS    CENTIMETEBS 


_ 

i:i 

- 

U 

£ 

IpinC  =lt) 

r 

a 

CUSIC 

0 

_      U 

XO — 

r- 

3 — 1 

20 

^ 

« 

;^ 2 

50 

^—3 

lrt.£jr.=60 

z 

r 

aOO 

ETERS 


1 

I'J  — 

1  3=20 

FUUlO 
Dh-ACHfllS 

cuorc 

CENTl 

1 

- 

^  — 

- 

3 

~ 

4 

^ 

5 

I 

S 

I 

— 

ORACHMS 

GRAMS 

; 

^ 



— to 

3 

Z 

*— 

— 

5 

i 

S 

I 



— 

• 

: 

3 

Lr  =  S 

1»=12-  ^ 

'~  l/l.03.  =  i 

Tlw  aqaivalents  of  fratftioas,  whethtfr  large  or  small,  may  lia  Rmnd  witll  great  nitfetj  by 
tteae  scales.  For  iastance.  .',  grain  =  H  o  f  thB  metric  emiivalenr,  of  T  grains,  and  1-aW  graitt 
=I-taOO  of  tHe  metric  equivalent  of  JO  grains.     Tliis  mettled  is,  of  course,  reversible. 

•243 


INDEX. 


ABDUCENS  nerve,  190 
Absorption,    general     principles 
of,  bO 
inflnence  of  leucocytes  on,  97    | 
in  the  large  intestines,  82 
in  the  small  intestines,  81 
in  the  stomach,  81 
of  fats,  82 
of  proteids.  81 
of  sugars.  82 
of  water  and  salts,  82 
paths  of,  81 

spectrum  of  oxyhsfimoglobin,  95 
Accommodation,  208 

range  of,  208 
Achroodextrin,  (50,  66 
Acid,  butyric,  50 
capric,  50 
caproic,  50 
glycocholic,  63 
hippuric.  46 
hydrochloric,  39 
myristic,  50 
oleic,  50 
palmitic,  50 
stearic,  50 
taurocholic,  63 
uric,  46 
Acquired  characters,  inheritance  of,  27 
Acromegaly,  53 
Action-current  in  the  muscles,  166 

in  the  nerves,  166 
Adenin,  46 
After-birth.  77 
After-images,  215 
After-sensation,  225 
After-taste,  224 
Agomogenesis,  23 
Agraphia,  203 
Air,  complemental,  137 
residual,  137 

respiratory  changes  in,  138 
stationary,  137 


Air,  supplemental,  137 

tidal,  i:;7 
Albuminoids,  derivation  of,  57 
digestion  of,  65 
nutritive  value  of,  86 
Albuminous  glands,  35 
Aldoses,  57 
Alexia.  203 
Alexine,  102 

Allonomous  equilibrium,  21 
Amnesia,  203 
Amphopeptones,  62 
Aujylodextrine,  60 
Amylopsin,  63 
Anabolism,  definition  of,  21 
Anelectrotonus,  156 
Animal  heat,  source  of,  14H 
Anode,  physical  definition  of.  156 
physiological  definition  of,  158 
Antilytic  secretion,  38 
Antipeptone,  62 
Antiperistalsis.  intestinal,  73 
Apex  beat.  107 
Apha.sia,  203 
Aphemia,  203 
Apnoea,  definition  of.  140 
Aqueous  humor,  207 
Articulations,  varieties  of.  77 
Asexual  reproduction,  23,  229 
Asphj-xia,  141 

stages  of,  141 
Assimilation,    general    characteristics 

of,  22 
Association  centres,  207 

fibres  of  the  cortex,  184 
Astigmatism.  210 
Atalectiisis.  133 
Atavism,  27 

Auditorv  nerve,   cochlear  portion  of, 
190 
vestibular  portion  of.  192 
Augmentor  centre  of  the  heart,  119 
Auricular  systole,  duration  of,  108 
245 


246 


INDEX. 


Aurieuloventricular  valves,  108 
Autonomous  equilibrium,  21 
Axone,  definitiou  of,  169 
length  of,  169 

BACTEEIAL  decomposition  in  the 
intestines,  64 
Banting  diet,  88 
Basophiles,  96 
Bile,  amount  secreted,  40,  63 

antiseptic  action  of,  64 

composition  of,  63 

relation  of,  to  fat  absorption,  64 

salts,  chemical  tests  for,  240 
Bile-acids,  63 

detection  of,  63 
Bile-pigmeuts,  63 

chemical  tests  for,  242 

origin  of,  63 
Bilirubin,  63 
Biliverdin,  63 
Biogen,  definition  of,  21 
Bioplasm,  definition  of,  21 
Biuret  test  for  proteids,  57,  240 
Blind-spot,  211 
Blood,  circulation  of,  105 

coagulation  of,  98 

distribution  of,  in  body,  92 

functions  of,  91 

globucidal  action  of,  102 

oxidations  in,  92 

period  of  ejection  of  the,  98 
of  reception  of  the,  99 

reaction  of,  92 

regeneration  of,  after  hemorrhage, 
101 

specific  gravity  of,  100 

total  quantity  of,  in  the  body,  91 

transfusion  of,  102 
Blood-corpuscles,  varieties  of,  102 
Blood-gases,  138 

tension  of,  139 
Blood-plasma,  color  of,  92 

composition  of,  92 
Blood-plates,  93 
Blood -pressui-e.  aortic,  121,  122 

capillary,  123 

changes  in,  122 

efi'ect  of,  on  renal  secretion,  42 

methods  of  measuring,  122 

origin  of,  122 
Bolometer,  165 
Brain,  blood  supply  of  the,  197 

growth  of  the,  195 

specific  gravity  of  the,  196 


Brain,  vasomotor  activity  in  the,  197 
Brain-weight,  decrease  of,  during  old 
age,  196 
method  of  determination  of,  194 
relation  of,  to  insanity,  194 

to  social  environment,  194 
table  of,  193 
Buffy  coat,  99 

pAFFEIN,  action  of,  on  kidneys,  47 
\J     Calcium     salts,     relation    of,    to 

blood  clotting,  100 
Calorie,  definition  of,  84 
Calorimeter,  148 
Calorimetric  equivalent,  149 
Calorimetry,  direct  and  indirect,  85, 

148 
Capsules,   suprarenal,    extirpation  of, 

52 
Carbohydrates,   absorption  of,   in  the 
intestines,  82 

chemistry  of,  57 

combustion  equivalent  of,  84 

digestion  of,  66 

in  the  intestines,  63 
in  the  stomach,  62 

dynamic  value  of,  87 

synthesis  of,  58 
Carbomonoxide  haemoglobin,  94 
Cardiac  centre,  187 

cycle,  analysis  of,  106 
definition  of,  106 
duration  of,  108 

nerves,  116 
Cardiopneumatic  movements,  138 
Catalvsis,  59 
Cell,  definition  of,  19,  20 

differentiation,  19,  20 

division,  23-30 
Cells,  growth  of,  23 

of  the  brain,  195 
Centre,  augmentor,  of  the  heart,  119 

cardiac,  187 

cardio-inhibitory,  119 

defecation,  75 

deglutition,  72 

for  muscle  sense,  227 

micturition,  76 

of  speech,  203 

respiratory,  160,  187,  237 

sweat,  48 

thermo-accelerator,  151 

thermogenic,  150 

thermo-inhibitory,  151 

thermotactic,  187 


INDEX. 


247 


Centre,  vasomotor,  12H,  187 
Ci'iitros,  association,  'JO"J 

in  tlif  nicdiiUa,  1S7 
('t'lfbcllniii.  illVcts  of  rinioval  of,   IH.'i 

functions  of,  l^.'i 
Cerebi'al   lieniisjiluTcs,    effects    of  re- 
moval of,  1W5 
relative  physiological  value  of,  185 
Cerumen,  48 
Characters,   acquired,  inheritance  of, 

27 
Chemotaxis,  32 
Chemotropisni,  32 
C'iieyne-Stukos  respiration,  136 
(."iiohi};;ogut'S,  10 
Chok'Sterin,  (J4 

of  sebaceous  secretion,  48 
Chyme.  62 

Circulating  proteid,  98 
Circulation,  fa?tal,  course  of,  235.  236, 
237 
types  of.  224 

of  the  blood,  104,  105 

of  the  brain  and  cord,  197 

of  the  lymph,  130 

l>nlni(inary,  127 

rate  of,  105 

renal,  42 
Coagulation  of  blood,  causes  of.  99 
conditions  necessary  for,  99,  100 
retarding  influences  affecting,  97, 

9S 
value  of.  99 
Coclilear  root  of  the   auditorv  nerve, 

190 
Coefficient  of  absorption  of  liquids  for 

gases.  1.30 
Color-blindness,  216 
Color  theories,  215 
Colostrum  corpuscles.  49 
Combustion  equivalent  of  foods.  84 
Common  sensation,  definition  of,  137 
Conceptions,  multiple.  237 
Condiments,  nutritive  value  of,  .58 
Conduction  by  contiguity,  160 

directions  of,  160 

process,  nature  of,  160 

rate  of.  161 
Conductivity,  definition  of,  18 

influences  afft-cting,  161 
Conjugated  sulphates,  46 
Conjugation,  26,  230 
Contractility,  definition  of.  IH 
Contractions,  introductory.  162 

normal  tetanic,  nature  of,  164 


Contracture,  definition  of,  Ui3 

from  fatigue,  163 

relation  of.  to  tctuniLS,  164 
Copulation,  2.3.3 
Cornea.  <'urvalure  of,  207 
Coronary  arteries,  circulation  in,  121 
Corpora  Aurantii,  109 

qnadrigemina,     functions     of     tin-. 
1.S7 
Corpuscles  of  the  blood,  93 

salivary,  60 
Ck)rtex    cerebri,    effects    of    localized 

stimulation  of.  182 
Cortical  areas,  motor,  182 
sensory,  184 

stimulation,  effect  of,  178 
Coughing,  145 
Cranial  nerves,  231 
Creatin,  46 
Creatinin,  46 
Cresol,  elimination  of,  46 
Crura,  lesions  of  the,  235 
Crystalline  lens,  207 
elasticity  of,  209 
Curara,  action  of,  153 
Currents  of  action,  diphasic  character 
of.  167 
in  muscle,  166 
in  nerves,  166 

of  rest,  165 
Cutaneous  sensations,  224 

DEATH  of  the  tissues,  33 
somatic,  33 
theory  of,  .32.  33 

Decomposition,  bacterial,  in  the  intes- 
tines, 64 

Defecation,  75 
cerebral  control  of.  75 

Degeneration    of    spinal     cord     after 
hemisection.  IhO 

Deglutition,  71 
centre  for,  72 
nervous  regulation  of,  72 
stages  of,  71 

Denmrcation  currents.  165 

Dendrites,  definition  of,  170 

Determination  of  sex,  theories  regard- 
ing, 2.38 

Deuteroprofeose.  definition  of,  61 

Dialysis,  definition  of.  ;i5 

Diapedesis,  97 

Di arthrosis.  77 

Diffusion,  definition  of,  .35 
of  impulses  in  the  cord,  176 


248 


INDEX. 


Digestion,  definition  of,  56 

gastric,  61 

intestinal,  62 

of  fats,  58,  66 

of  proteids,  65 

of  starch,  60-66 

panci-eatic,  62 

salivary,  60 

summary  of,  65 
Digitalis,  action  of,  on  the  kidneys,  47 
Diplopia,  210 
Diuretics,  action  of,  44 
Dropsy,  130 
Du  Bois-Eeymond's  law,  155 

I  EJACULATION,  233 
J     Electrical  phenomena  in  muscle 
and  nerve,  156,  157,  158 
Electrotonic  changes,  156 

current,  definition  of,  167 
Emraetropia,  208 
Endocardiac  pressure  curves.  111 
Energy,  potential,  of  foods,  84 
Enzyme  action,  theories  of,  59 
Enzymes,  classification  of,  60 

composition  of,  59 

definition  of,  59 
Eosinophiles,  96 
Epigenesis,  theory  of,  28 
Epinephrin,  52 
Equilibrium,  allonomous,  21 

autonomous  21 

carbon,  29 

of  the  body,  definition  of,  221 

nitrogenous,  86 

sense  of,  222 
Erythroblasts,  96 
Erythrocytes,  93 
Erythrodextrin,  60 
Eupnoea,  definition  of,  140 
Excitation  wave,  cardiac,  113 
Excretion,  definition  of,  35 
Exercise,  efi"ect  of,  on  growth,  23 
on  metabolism,  89 
on  pulse-rate,  108 
Exhaustion,  160 
Expiration,  forced,  movements  of,  135 

muscles  of,  135 
Eye,  functions  of,  206 

positions  of,  207 

FACIAL  nerve,  199 
Faeces,  composition  of,  65 
Far-point,  208 
Fat,  combustion  equivalent  of,  84 


Fatigue,  cause  of,  160 

of  muscle,  160,  163 

of  nerve,  160 

production  of,  196 
Fats,  absorption  of,  63,  82 

chemistry  of,  58 

composition  of,  58 

digestion  of,  63,  66 

dynamic  value  of,  88 

nutritive  value  of,  88 

origin  of,  in  the  body,  88 
Fechner's  law,  224 
Fehling's  solution,  240 
Fermentation  test,  240 
Fertilization,  26,  231 

significance  of,  26,  27 
Fibrin,  99 

ferment,  98 

origin  of,  100 
Fibrinogen,  98,  99 
Filtration,  definition  of,  35 
Food,  combustion  equivalent  of,  84 

composition  of,  56 

definition  of,  22 

dynamic  value  of,  84 
Food-stufis,  classification  of,  56 
Foramen  ovale  in  the  fcetal  heart,  236 
Fovea  centralis,  212 
Franklin  theory  of  color  vision,  215 
Furfural,  64 

GAMOGENESIS,  26 
Gases  in  the   blood,   respiratory 
changes  in,  139 
poisonous  inhalation  of,  140 
Gastric  digestion  of  proteids,  61 
juice,  acidity  of,  61 
compositioii  of,  61 
secretion,  eflect  of  the  diet  on,  39 
normal  mechanism  of,  39 
stimulants  for,  39 
Germ-plasm  as  a  basis  of  heredity,  27 
origin  of,  27  28 
structure  of,  28 
Gestation,  dui-ation  of,  237 
Gland,  mammary,  48 
pancreatic,  39 
parotid,  35 
sublingual,  35 
submaxillary,  35 
thyroid,  efiects  of  removal  of,  50 
Gland-cells,  activity  of,  during  secre- 
tion, 35 
mammary,  histological  changes  in, 
50 


INDEX. 


249 


QIaiids,  albuminous,  secretion  from,  3.') 

elcctriral  clianjii.'s  in,  37 

gastric,  iS"^ 

intestinal,  II 

laclirynial,  -11 

niucuus,  secretion  from,  '.]iy 

sweat,  IS 

elTect  of  exercise  on,  48 
of  iieat  on,  48 
Glol)in,  !»:{ 

tilobuciilal  action  of  tiic  blood,  10'2 
Cilonuruli,    renal,   secretory   function 

of,  43 
Glossopharyngeal  nerve,  19:2 
Glycogen,  amount  of,  in  the  liver,  87 
in  muscle,  87 

function  of,  87 

of  the  liver,  52 

reserve  store  of,  87 

test  for,  240 
Gmellin's  reaction,  ()3,  240 
Gra])liic  niutluxl  of  studying    muscu- 
lar contractions,  61 
Growth,  inrtuence  of  exercise  on,  2.'5 
of  temperatui'c  on,  31 

of  brain,  195 
Guanin,  46 

H.EMATIN,  93 
rittniatopoiesis,  96 
ILvniiii.  91 
Hicniochroniogcn,  93 
Haemoglobin,  93 

compounds  of.  with  gases,  94 

decomposition  products  of,  93 

oxygen  capacity  of,  93 
Hallucinations,  201 
Hearing,  219 

subjective,  220 
Heart,  anannia  of.  120 

augmentor  nerves  of.  117 

changes  in  form  of,  106 

compensatory  pause  of.  116 

electrical  changes  of,  113 

fibrillary  contractions  of.  120 

muscle,  refractory  jieriod  of,  116 
rhythmicity  of.  113 

nerves  of,  IKi 

nutrition  of.  120 

work  done  by,  110 
Heart-beat,  conduction  of,  from  auri- 
cles to  ventricles,  105 

heat  produced  by,  105 

rate  of.  108 
Heart-sounds.  107 


Heat-centres,  151 

Heat-dissipation,  estimation  of,  149 
Heat-production,  estimation  of,  149 
Heat,  source  of,  l.")l 
Heller's  test,  .")7 
Heuiipeptone,  62 

Hemisection  of  cord,  degeneration  fol- 
lowing in.  180 
l)hysiological  eH'cct  of.  IHI 
Hemorrhage,  fatal,  limits  of,  101 

regeuei-ation  of  l)lood  after,  101 

relation  of,  to  blood  jircssure,  101 

Siiline  injections  after.  101 
Heredity,  definition  of.  27 

physical  basis  of,  27 

theories  of,  27 
Hering's  theory  of  color  vision,  215 
Heteroprotcose,  61 
Hibernation,  199 
Hiccough,  145 
Hipi)uric  acid,  amount  of,  in  urine,  46 

source  of,  46 
Histon,  98 

Hofacker-Sadler  law,  238 
Homothcrmous  animals,  148 
Hunger,  227 

Hydrochloric    acid    of     the    gastric 
juice,  39 
secretion  of,  39 
source  of.  39-61 
test  for.  61 
Hypermetropia.  209 
Hypcrpncea,  definition  of,  140 
Hypnotism,  199 
Hypoglossal   nerve.  193 
Hypoxanthin.  46 

IMPREGNATION.  231 
Indol,  elimination  of,  46 
Induction  apparatus,  schema  of.  154 
Infections,  intra-uterine,  27 
Inhibitory  centre,  cardiac.  119 
respiratory.  1 13 
nerves  of  heart.  IKi 
of  pancreas,  40 
of  respiration.  143.  144 
of  salivary  glands.  37 
of  stomach.  .39 
Inorganic  salts  of  the  blood,  98 
Internal  secretion,  definition  of.  .3.5 
Intestines,  absorption  in.  81 
innervation  of.  7.") 
peristaltic  movements  of.  73 
rhythmic  movements  of,  75 
Intracranial  pressure,  197 


250 


INDEX. 


Intraocular  images,  211 
Intrapulmonary  pressure,  134 
Intravascular  clotting,  100 
Introductory  contractions,  162 
Invertase,  64,  66 

Iodine  reaction  for  starch,  58,  240 
lodothyrin,  51 
Iris,  162 
Irradiation,  217 
Irritability,  definition  of,  18 
Irritants,  classification  of,  154 
Isodyuamic  equivalence  of  foods,  85 

JAUNDICE,  40 
Joints,  classification  of,  77 
movements  of,  77 

KAEYOKINESIS,  23,  26 
Katabolisra,  definition  of,  21 
Katelectrotonus,  156 
Kathode,  physical  definition  of,  156 

physiological  definition  of,  158 
Rations,  162 
Ketoses,  57 
Kidneys,  blood-flow  through,  42 

internal  secretion  of,  53 

vasomotor  nerves  of,  42 
Knee-jerk,  centre  for  the,  199 

significance  of,  200 

variations  of,  200 
Kymograph,  122 

LABOE,  nature  of,  81 
physiological  division  of,  20 
Langerhans,  bodies  of,  39 
Language,  -79 
Larynx,  78 

Latent  areas  of  the  cortex,  184 
period  of  muscle,  162 
of  reflex  actions,  176 
of  retinal  stimulation,  214 
Laughing,  146 
Leucin,  formation  of,  62 
Leucocytes,  93 
classification  of,  96 
functions  of,  97 
movements  of,  97 
Leucocytosis,  97 
Leuconuclein,  100 
Life,  general  hypothesis  of,  32 
Liver,  extirpation  of,  46 
internal  secretion  of,  52 
urea  formation  in,  45 
Living  matter,  electrical  energy  of,  165 
inhibition  of,  32 


Living  matter,  molecular  structure  of, 
20,  21 
results  of  stimuli  on,  28,  29 
Localization  of  cortical  cell-groups  for 
aS"erent  impulses,  182 
of  touch-sensations,  225 
Locomotor  mechanisms,  77 
Lymph,  composition  of,  102 
movements  of,  103,  130 
origin  of,  102 
pressure  of,  103,  130 
physical  properties  of,  102 
Lysatinin,  relation  of,  to  urea  forma- 
tion, 46 

MACULA  lutea,  212 
Maltase,  66 
Maltose  in  starch  digestion,  60 
Mastication,  71 
Medulla,  centres  in  the,  187 

functions  of  the,  187 
Menopause,  232 
Menstruation,  232 

age  of  onset,  231 

cessation  of,  232 

relation  of  ovulation  to,  233 

theory  of,  232 
Metabolism,  83 

definition  of,  21 

determination  of,  89 

during  sleep,  90 
starvation,  90 

efiect  of  temperature  on,  90 

intensity  of,  in  the  brain,  197 

internal  self-adjustment  of,  21 
Metric  system,  242 
Microcytes,  93 
Micturition,  75 

centre  for,  76 

nervous  mechanism  of,  76 
Milk,  composition  of,  49 

reaction  of,  49 
Millon's  test  for  proteid,  240 
Moore's  test,  240 

Motor  areas,  degeneration  of,  after  re- 
moval, 183 
physiological  characters  of,  182 
Mucous  glands,  35 
Multiple  conceptions,  237 
Muscse  volitantes,  211 
Muscles,  absolute  force  of,  165 

action-currents  in,  166 

exhaustion  of,  160 

fatigue  of,  160 

irritability  of,  153 


INDEX. 


251 


Muscles,  latent  i>orlod  of,  Ki'J 

reaction  in,  loS 
Muscrlc-cnrrents.  asccn<lin;,',  l.'ifi 

tlcscentiin;;,  l.">fi 
Musck'-sotinds,  Kil 
Muscular  contractions,  loH 

Krapliic  nietiiod  of  studying;,  Uil 
source  (»r  energy  in,  lt)."> 
exen'isc,  clVect  of,  on  ^rowtii.  "J.'J 
ou  nietabolisiu,  81) 
on  pulse-rate,  10b 
on  sweat  jilauds,  48 
sense.  227 
Musical    sounds,    characteristics    of, 

221 
Myogram,  161 
Mvo-tra])!),  KU 
Myopia,  208 
Myosin,  168 

ferment,  168 
Myosiiioi^'en,  167 
Myx<rdenia.  ~A 

VTEAR-POINT  of  vision,  208 
x\      Xegative  after-iniafio,  215 
impulse,  107 
variation,  166 
Nerve  centre,  definition  of,  202 

chorda  tymjiani,  .'57 
Nerves,  alxlucens,  190 

action-currents  in,  166 

auditory,  190 

cardiac,  116 

degeneration  of.  ir)9 

facial.  190 

gloss()i)harynt£eal,  192 

hypoglossal,  193 

influences  aflfectiug    irritabilitv  of, 
1.59 

olfactory.  188,  22.3 

optic.  188 

pathetic,  188 

pneumogastric,  193 

spinal  accessory,  193 

trigeminal,  190 

vasomotor,  127 
Nervi  erigentes,  233 
Neurone,  definition  of,  169 
Neurones,  afl'erent,  171 

central,  173 

efTerent,  171 
Neutroiihiles,  06 
Nitrogenous  eiinilihrium,  86 

proximate  i)rinciples,  68 
NcBud  vital,  193 


I  Non-nitrogenous     proxinnitc     princi- 
I      ]iles,   69 
Nnciius,  definition  of,  19 

fn  net  ions  of,  22,  2.''. 
Nnlrilion,  definition  of,  Itt 
Nutritive  value  of  .ilhuminoida,  86 
of  carlxdiyd  rates,  87 
of  condiments,  .Vi 
<if  fats,  88 
of  proteids,  8.5 
of  salts,  88 
of  water,  88 

OLFACTORY  nerves,  188,  223 
Oncometer,  42 
Optic  nerves,  188,  214 

thalami,  functions  of,  186 
lesions  of  the,  186 
Organ  of  C'orti,  220 
Origin  of  life,  32 
Osniipsis,  definition  of,  3.5 

relation  of,  to  secretion,  .35 
Osteomalacia,  53 
Ovaries,  internal  secretion  of,  .53 
Ovulation,  231 
Ovum.  231 

fertilization  of,  231 

maturation  of.  231 

segmentation  of,  234 
Oxygen  tension  in  the  blood.  1.39 
Oxyhasmoglohin,  94 

PAIN,  227 
Pancreas,  extirpation  of,  51 
grafting  of,  51 
histology  of,  39 
innervation  of,  40 
internal  secretion  of.  51 
Pancreatic  juice,  amvlolvtic  action  of, 
63 
composition  of,  62 
fat-splitting  jiower  of,  63 
Paralytic  secretion,  38 
Paramyosinogen,  168 
Parthenogenesis.  26 
Parturition.  76 

sjjinal  centre  for,  77 
Pathetic  nerve.  188 
Pepsin,  (il 

Peptones,  absorption  of.  in  the  intes- 
tines, 81 
in  the  stomach.  81 
definition  of,  (il 
Peristaltic   movemeuts   of  the   intes- 
tines, 73 


252 


INDEX. 


Perspiration,  amount  of,  47 

character  of,  47 

constituents  of,  48 

insensible,  48 
Pettenkofer's  test,  63,  240 
Pfliiger's  law,  158 
Phenol,  elimination  of,  46 
Physiological  division  of  labor,  20 
Physiology,  aim  of,  18 

definition  of,  17 

history  of,  17,  18 

subdivisions  of  17 
Pituitary  body,  extirpation  of,  53 

extracts,  action  of,  52 
Placenta,  77 

Placental  circulation,  235 
Plant-cells,  assimilation  in,  22 
Plasma  of  blood,  97 
Plethysmograph,  110 
Pneumogastric  nerves,  193 
Pneumograph,  136 
Poikilothermous  animals,  148 
Polar  bodies,  231 

Polarizing  current,  effect  of,  on  mus- 
cle, 162,  163 
Polypnoea,  definition  of,  140 
Polyspermy,  234 
Positive  after-image,  215 
Postganglionic    fibres  of   the  sympa- 
thetic system,  176 
Preganglionic    fibres    of   the    sympa- 
thetic system,  176 
Presbyopia,  209 
Pressure,  cardiac,  110 

intracranial,  197 

intrathoracic,  133 

intraventricular,  110 

sense,  224 
Primary  vision  centre,  214 
Proteid,  circulating,  definition  of,  85 

tissue,  definition  of,  85 
Proteids,  chemical  tests  for,  240 

classification  of,  57 

color  reactions  of,  57,  240 

combustion  equivalent  of,  84 

digestion  of,  62-65 

general  reactions  of,  57 

molecular  structure  of,  56 

nutritive  value  of,  85 

of  the  blood,  93 
Proteoses,  definition  of,  61 
Prothrombin,  100 
Protoplasm,  properties  of,  18,  19 
Ptyalin,  37 

action  of,  60 


Pulse,  arterial,  107 

cause  of,  124 

characters  of,  124 

dicrotic  wave  of,  125 

speed  of,  126 

tension  of,  124 

volume  of  the  heart,  110 
Pupil,  changes  in,  during  accommoda- 
tion, 208 
Pupillary  reflex  to  light,  210 

REACTION  of  degeneration,  159 
time,  201 
Reduced  reaction  time,  201 
Eeflex  action,  simple,  173 
path  of,  173 
time  value  of,  201 
Reflexes  iu  man,  175 
latent  period  of,  176 
spinal,  178 

inhibition  of,  178 
reenforcement  of,  178 
summation  of  stimuli  in,  176 
vasomotor,  origin  of,  139 
voluntary  control  of,  176 
Refractory  period  of  the  heart,  116 
Rennin,  action  of,  on  milk,  62,  67 

of  the  kidneys,  62 
Reproduction,  asexual,  23,  229 
definition  of,  18 
methods  of,  229 
of  living  matter,  23 
sexual,  23,  26,  229 
Residual  air,  definition  of,  137 
Respiration,  associated  movements  of, 
136 
definition  of,  133 
nervous  mechanism  of,  143 
rhythm  of,  136 
Respiratory  centres,  143,  187,  237 
movements,  duration  of,  137 
effect  of,  on  blood  pressure,  141 
frequency  of,  137 
nerves,  143-145 
pauses,  136 
pressure,  134 
quotient,  87,  138 
sounds,  136 
Retinal  images,  inversion  of,  219 
stimulation,  after  effects  of,  214 
latent  period  of,  214 
Reversion  to  ancestral  characters,  27 
Rhythmic   activities    of   the   central 
nervous  system,  197 
of  the  heart,  113 


ryoKX. 


253 


Rhythmic  movements  of  the  spleen, 

5-1 
Rigor  caloris,  168 
mortis,  1(>7 
coiitractiirt'  of.  1(>7 
inlliicMcu  of  nervous  system  on, 

17H 
nature  of  changes  in,  1(57 
Running,  7s 

SALIVA,  composition  of,  t>0 
proiH-rties  of,  tJO 
source  of,  3.") 
uses  of,  (JO 
Salivary  cori)uscles,  HO 
glands,  ner\es  of,  37 
secretion,  action  of  drugs  on,  38 
cerebral  control  of,  37 
normal  mechauisni  of,  S8 
Salts,  calcium,  uses  of,  s9 
elimination  of,  88 
inorganic,  of  the  urine,  47 
nutritive  value  of,  58,  88 
of  iron,  importance  of,  89 
Schenk's  theory,  2:iS 
Sebaceous  secretion,  48 
Secreting  glands,  histological  changes 

in,  3G,  37 
Secretion,  antilytic,  38 
biliary,  40 

circulatory  factors  in,  37 
definition  of,  34 
gastric,  39 
intestinal,  41 
mammary.  48 
pancreatic.  40 
paralytic,  3::* 
salivary,  35 

action  of  drugs  on,  38 

cerebral  control  of,  37 

sebaceous,  character  of,  48 

function  of,  48 
sweat,  47 
thyroid,  50 
urinary,  42 
Secretions,  general  characteristics  of, 

:J4,  3.-> 
Secretorv  nerves,  mofle  of  action  of, 
37,  38 
of  kidney,  42 
of  liver,  40 
of  pancreas,  40 
of  stomach.  3!) 
of  sweat  glands,  48 
Segmentation,  2.'U 


Seiiiiliinar  valves.  108 
Sensation,  common,  definition  of,  224 
.  Sense  of  touch,  '22ii 
Sensory  cortical  areas,  motor  responses 
I      from,  1*1 
Sex  of  olTspring,  determination  of,  238 
.  Sexual  characters,  2^J0 

elements.  230 
I      reproduction,  23,  2(i,  229 
!  Shivering,    l.">0 
!  Shock,  nature  of,  173 
Sighing,  145 
Singing,  115 

Skatol.  elimination  of,  46 
Sleep,  cause  of.  I!t7 

condition  of  the  pupils  in,  198 
effect  of  loss  of.  198 
on  metabolism,  90 
'  Smegma  prseputii,  48 
i  Smell.  222 
;  Sneezing,  145 
Sniffing,  146 
Sobbing,  146 

Sodium  chloride,  amount  of,   in  the 
I      urine,  47 
Somatic  death,  :i3 
Speaking,  115 

Specific  gravitv  of  urine,  44 
Spectrum,  95,  96 

;  Speech,  dependence  upon  hearing,  203 
j      elements  of,  202 
i  Speech-centre,  203 
I  Spermatids.  230 
'.  Spermatocyte,  230 
!  Spermatozoa,  movements  of,  230 
Sphj-gmogram,  125 
Sphygmograph,  125 
Spinal  accessory  nerve,  193 
cord,   degeneration  of,  from  hemi- 
section,  ISO 
results  of  section  of  the,  187 
weight  of,  195 
Splanchnic  nerves,  gastric  fibres  of,  39 
influence  of,  on  bile  secretion,  40 
on  blood  pressure,  119 
Spleen,  function  of,  53 

rhythmic  movements  of,  54 
vasomotor  nerves  of,  54 
Staircase  contractions,  162 
Standing,  78 

Starch,  chemical  test  for,  58,  240 
digestion  of,  60,  63 
hydrolysis  of,  .58 
Steapsin,  63 
Stensou's  experiment.  1.59 


254 


INDEX. 


Stimulation  of  the  cortex,  178 
Stimuli,  classification  of,  28 
definition  of,  154 
efi"ect  of  changing  intensity  of,  155 

varying  strength  of,  155 
results  of,  on  living  matter,  28,  29 
Stomach,  absorption  in,  81 
glands  of,  39 

immunity  of,  to  its  own  secretion,  67 
innervation  of,  72 
movements  of,  72 
Strabismus,  210 
Succus  entericus,  64 
ferments  of,  64 
Sucking,  146 

Sugars,  absorption  of,  in  the  intestines, 
82 
in  the  stomach,  81 
chemical  tests  for,  240 
Supplemental  air,  definition  of,  137 
Suprarenal  capsules,  52 
Suture,  77 

Sympathetic  nerves,  cardiac  fibres  of, 
116 
postganglionic  fibres,  176 
preganglionic  fibres,  176 
secretory  fibres,  to  pancreas,  40 
to  salivary  glands,  37 
to  stomach,  39 
stimulation,  efiect  of,  on  heart,  117 
Symphysis,  77 
Syndesmosis,  77 
Synovial  fluid,  41 
Syutonin,  61 
Systole,  auricular,  108 
ventricular,  105 

TACTILE  areas  of  the  skin,  225 
Taste,  nerves  of,  223 
organs  of,  223 
Taste-buds,  223 
Taste-sensations,  223 
Tears,  41 
Temperature,  effect  of,  on  growth,  31 

nerves,  226 

postmortem  rise  of,  151 

sense,  226 

variations  of,  148 
Tension  of  the  blood  gases,  139 
Testes,  internal  secretion  of,  52 
Testicular  extract,  eflTect  of,  53 
Tetanus,  analysis  of,  164 

secondary,  167 
Thernio-accelerator  centres,  151 
Thermogenesis,  150 


Thermogenesis,  mechanism  of,  150 
Thermo-inhibitory  centres,  151 
Thermolysis,  150 

mechanism  of,  151 
Thermopile,  165 
Thermotactic  centre,  187 
Therm  otaxis,  150 
Thirst,  227 

Thiry-Vella  fistula,  64 
Thymus  gland,  53 
Thyroidectomy,  50 
Thyroids,  function  of,  51 

grafting  of,  51 

internal  secretion  of,  51 
Tidal  air,  definition  of,  137 
Tissue  proteid,  85 
Tonus,  muscular,  in  the  insane,  177 

reflex  origin  of,  176 
Transfusion  of  blood,  102 
Traube-Hering  waves,  129 
Trigeminal  nerves,  189 
Trommer's  test,  240 
Trophic  nerves  of  the  salivary  glands, 

38 
Trypsin,  62 
Trj'ptic  digestion,  products  of,  62 

value  of,  62 
Tyrosin,  formation  of,  62 

UEEA,  amount  of,  in  the  urine,  45 
antecedents  of,  45 
elimination  of,  44 
formation  of,  in  the  liver,  58 
origin  of,  in  the  body,  45 

in  the  liver,  45 
preparation  of,  from  proteid,  45 
presence  of,  in  the  sweat,  48 
Uric  acid,  formation  of,  in  the  liver,  46 

origin  of,  in  birds,  46 
Urine,  acidity  of,  44 
constituents  of  the,  45 
estimation  of  solids,  44 
secretion  of,  43 
specific  gravity  of,  44 
Urobilin,  44 

VAGUS,  afferent  fibres  of  the,  193 
cardiac  fibres  of,  116 
effect  on  heart,  119 
gastric  branches  of,  39-72 
respiratory  function  of,  145 
secretory  fibres,  to  pancreas,  40 

to  stomach,  39 
stimulative  effect  of,  on   heart, 
116 


IXPhX. 


Valves,  iiuriculovoiitricular.  inr> 

sciiiilmiar,  HI.")  Ids 
N'alvulii'  roiinivoiiti'S,  value  of,  in  ab- 
sorption, 81 
Vasoconstrictor  nerves,  definition  of, 

1J7 
\a.so(lilator  ncrve.s,  dclinilion  of,  127 
Viusoniotor  centre,  187 
inedullary,  128 

centres,  spinal,  128 
synipatlietic,  128 

nerves,  127 

reflexes,  orifiin  of,  129 
Vein,  entrance  of  air  into,  124 

pulsation  in,  cause  of,  110 

reual,  eflect  of  compression  on  uri- 
nary secretion,  44 
Vena?  f  hcbesii,  120 
Venous  jiulse,  resjtiratory,  123 
Ventricular  systole,  duration  of,  108 
Ventrilotiuism,  221 
Vernix  caseosa,  48 

Vestibular  root  of  auditory  nerve,  192 
Vision,  binocular.  218 

clearness  of,  219 
Visual  purple,  212 
Vital  capacity  of  the  lungs,  137 
Vitreous  humor,  207 
Voice,  79 

pitch  of,  79 


Voice,  register  of,  79 

V(»luntarv  reactions,  afferent  paths  rif, 

178 
Vomiting,  73 

causes  of,  73 

centres  for,  73 

nervous  mechanism  of,  73 

WALKING,  7H 
Wandering  cells,  definition   of. 
97 
Water,   amount    lost   tliroujih    lungs, 
138 
elimination  of,  4() 
imbibition  of,  88 
nutritive  value  of,  88 
Weber's  law,  224 
I  Whispering,  79 
I 

XANTHIN,  4B 
Xantho-proteic  reaction.  240 

YAWNING.  M(! 
Young-Helinboltz  theory  of  color 
vision,  215 

ZOLLNER'S  lines,  217 
Zymogen  granules,  definition  of, 
■37 


COLUMBIA  UNIVERSITY 

This  hook  is  due  on  the  date  indicated  below,  or  at  the 
expiration  of  a  definite  period  after  the  date  of  borrowing, 
as  provided  by  tlie  rules  of  the  Library  or  l:)y  special  ar- 
rangement with  the  Librarian  in  charge. 

DATE  BORROWED 

DATE  DUE 

DATE  BORROWED 

DATE  DUE 

C28!e38)M50 

QP40 
Guenther 


G93 


